"THEM THAT BELIEVE" refers to ONLY the APOSTLES.

Reason 1:  Context is the Apostles' Unbelief in Christ's resurrection.
In Mark 16:14, Jesus rebukes the apostles for their unbelief in His resurrection.
In v. 11-14, four times the apostles' unbelief is mentioned as Jesus addressed the apostles:
v.11 "They (apostles), when they had heard that he was alive ......believed not".
v.13 "...neither believed they them".
v.14 "He...upbraided them (apostles) with their unbelief and hardness of heart".
v.14 "...because they (apostles) believed not them which had seen him after he was risen".

After this rebuke Jesus gives the apostles the Great Commission in v.15,16.  Once the commission is given, Jesus returns to his immediate audience of the eleven apostles when He says in v.17,18 "These signs shall follow them that believe" (ie. those of you eleven apostles who believe in my resurrection).

In my name:
1.  they shall cast out devils.
2.  they shall speak with new tongues.
3.  they shall take up serpents.
4.  if they drink any deadly thing, it shall not hurt them.
5.  they shall lay hands on the sick and they shall recover.

Reason 2:  Practical Experience shows that promises 3, 4, 5, are not true for every believer today. In spite of continued failure to heal Charismatics still think that these 5 promises are for every believer today. 
The obvious problem with this interpretation is that it does not deal with everything mentioned in the text.

a)  No Charismatic can always fulfill the 5th promise.  It says that they shall lay hands on the sick and they shall recover.  This means 100% recovery all the time.  No one can do this today, as the apostles could in Acts 5:12-16.
 "By the hands of the apostles were many signs and wonders wrought among the people...they (believers) brought forth the sick into the streets... and they were healed every one".  v. 16.
John Wimber, a famous Charismatic, laid hands on 250 Down's Syndrome children and none were healed.
Reinhard Boncke tried to heal over 200 Kenyans and none were healed at a meeting at Kisumu.

b)  "If they drink any deadly thing, it shall not hurt them".
"If" means accidentally.  The problem is that many good Christians have become sick or died by poisoning.  Have you as a believer ever vomited?

c)  "They shall take up serpents".
We ask a Charismatic to take up a deadly snake.  He replies by saying: "No, that would be tempting God."  Yet in the first century this was a sign that the apostles did (shall do) to prove the Word of God and their authority.  Some believers today have died in trying this.  Hence showing that this is not for today.

Reason 3:  AORIST tense of "believe" in Mark 16:17 refers to those who did believe in the past, not who will believe in the future.
"These signs shall follow them that believe."  The Greek word for believe here "pisteusasin" which is in aorist participle referring to those who did believe in the past".
[S. Zodhiates, "Complete New Testament Word Study Dictionary" p. 1107]
"not those who would believe in the future".
[S. Zodhiates, "Hebrew-Greek Key Word Study Bible" p.1223]
The aorist tense refers to a past action at a point in time, not an event that recurs again into the future, as it would be if it was true of all believers.

Reason 4:  Belief (pisteusasin in Mark 16:17) does not refer to saving belief.  In John 3:16 and 5:24 saving belief is "pisteuwn", a different word ending.  Hence, "belief" in Mark 16:17 refers not to all future believers, but to the apostles believing in Christ's resurrection at a point in time, once for all time.

Reason 5:  "Do all speak with tongues?"  1 Corinthians 12:30, requires the answer "No, not all believers have the gift of speaking with tongues".

Reason 6:  The Purpose of these signs was to confirm the Word of God spoken and written by the apostles as Mark 16:20 says.
"And they (apostles) went forth and preached everywhere, the Lord working with them (apostles), and confirming the Word with signs (eg. tongues) following".
Once the Word of God (the New Testament) had been confirmed by the apostles' signs, then further signs were not needed.  The signs had done their job of proving the New Testament as being from God.  When the Word of God was completed, then miraculous Apostolic confirmatory signs were no longer needed.

Reason 7:  Mark 16:20 continues the context to mean apostles.

This describes what happened to the apostles after they changed from unbelief in Christ's resurrection to believing it and preaching it everywhere with signs following.
Hence in v.20, the context is still only the apostles doing signs, not every believer doing signs.

Conclusion.  Either all 5 signs are valid for today or none are valid today.  They only refer to first century apostles.

Reason 8:  Tongues had ceased by 70 AD because their use is only mentioned in the earlier New Testament books, such as Mark 16 (57 AD), Acts (54 AD), 1 Corinthians (57 AD).
In all the latter books, tongues are never mentioned.
Why?  Because they never happened after 70 AD and were of no relevance to any churches thereafter.  Tongues are never commanded in any New Testament book for believers to practice.
1 Corinthians 12, 13, 14 rebukes the Corinthians wrong use of tongues.  It is not endorsing tongues to be practiced.  Charismatics think that the key to spirituality is tongues, a phenomena that is not mentioned in 24 out of 27 New Testament books.

Why are tongues ABSENT from 2 Corinthians to Revelation?  If tongues were so necessary, you would definitely see them in the rest of the New Testament.
The book of Romans, which is well-known as the most complete summary of Christian doctrine and practice in the Bible, does not once mention tongues.  Why not?  Because tongues, by the time Romans was written (60 AD) was almost finished as a gift and would be of no relevance in the Church age after 70 AD when God judged Jerusalem.
Think about it, if tongues were important, God would have mentioned them at least once in Romans, or 2 Corinthians, or Galatians, or at least in one letter to a church in a positive context.

Reason 9:  The gift of tongues was never endorsed or practiced by early church leaders.  

Clement of Rome in 95 AD wrote a letter to the Corinthian church rebuking every problem that Paul rebuked except tongues.  Why did he not mention tongues or miracles? 
Justin Martyr (160 AD) visited many churches but never once mentions tongues, not even in his lists of spiritual gifts.
Origen (250 AD) in his voluminous writings never mentions tongues, but argues against Celsus that the sign gifts of the apostles' age were temporary and were not exercised by Christians in the 3rd Century.
Chrysostom (347-407 AD) commented on the 1 Corinthian passage:  "This whole place is very obscure:  but the obscurity is produced by our ignorance of the facts referred to and by their cessation, being such as then used to occur but now no longer take place."  [Homilies, XXIX, 1]
Augustine (354-430 AD) said in speaking of Acts 2:4, "In the earliest times, the Holy Ghost fell upon them that believed: and they spake with tongues...these were signs adapted to the time.  For there behooved to be that betokening of the Holy Spirit...that thing was done for a betokening and it passed away."

Reason 10: "Now abideth faith, hope, charity, these three..." 1 Corinthians 13:13.
Now (57AD) abides (continues) faith, hope, charity, these three" (not "these six prophecy, tongues, knowledge").
Since faith and hope finish at Christ's return, then prophecy, tongues and knowledge had to have finished by 96 AD because they were not abiding, but declining in 57 AD.

How To Protect Your Loved Ones!

It is surely the case that we are today seeing a spawning of satanic cults in a measure almost beyond comprehension and new cults are beginning with every week that passes. Clever individuals with a smattering of religious knowledge are emboldened by their own pride and motivated by Satan to press for their own piece of influence into today's religious scene. In the face of all of this, concerned people are asking as never before what they can do to protect themselves and their loved ones from these terrible subversive religious influences.

1. Understand Christian doctrine. The chief single reason for the success of the cults is the spiritual naivete on the part of many. Too many Christians are content with a superficial knowledge of the Word of God and think of themselves as thereby being spiritually intelligent. Nothing could be farther from the truth!

The Christian must understand the Bible from a doctrinal point of view. We live in a time when doctrine has been played down in favour of Christian experience. This is the most foolish course imaginable because experience has little or nothing to do with Christian truth. Our experiences are merely human. They are the responses of our nervous system to spiritual truth or error that impinges on our minds and hearts.

The evangelical leader who says, "We do not need more doctrine, but more experience" should rethink his statement. He is playing into the hands of the cultic wolves who prowl on the edges of the flock. The simple lambs who pursue additional feelings may get their titillation from the big, bad, but friendly wolf.

2. Separation from spiritual subversion. The Apostle Paul carefully warned the Ephesians, "Have no fellowship with the unfruitful works of darkness" (Ephesians 5:11).

An inquiry into the nuances of false doctrine is an endless pursuit indeed. Few people have the time or the available energy to know all that can be known about the myriad of false religious philosophies of our time. It is not true that we cannot speak critically of false doctrine unless we have read everything that the leadership of these cults has to say. One only has to eat a good steak to realize that the contents of a thousand garbage cans are simply beneath his standards.

There are foolish Christians who are too inquisitive. The statement that says, "You cannot know what it is until you have tried it" is a satanic doctrine, and it is the very one that he used to subvert Eve and bring the terrible cancer of sin into all of the world.

3. Refuse profane points of view. These are the very words with which Paul advised Timothy, "Refuse profane and old wives' fables" (1 Timothy 4:7). The Apostle Paul was aware that the world would be filled with spiritual exhibitionists and religious lunatics who would tie up the time and energy of anyone willing to listen to them, doing this for hours and even days.

We live in a time in which stories come to us about pictures of Christ in the clouds, resurrections in remote jungle areas, preachers in some obscure town with a new and unheard of doctrine -- the stories are endless.

Christians are enjoined not to give themselves to these things but rather to follow the good advice also extended to Timothy, "Give attendance to reading, to exhortation, to doctrine" (1 Timothy 4:13). Further, we are called upon to "meditate upon these things; give thyself wholly to them, that thy profiting may appear to all" (1 Timothy 4:15).

It is clear then that the Christian must not float through life on the wave of some existential euphoria. Rather the Scripture commands again and again that he must be careful, take heed, watch, remember. He is called upon to be very sober because his satanic adversary continues to go about seeking whom he may devour (1 Peter 5:8).

4. Do not encourage cultic practitioners. The Christian is supposed to be loving in his attitude towards people, but he must also face the hard truth that many deceivers have come into the world who do not believe the Gospel of Jesus Christ and are in fact enemies of the Lord. They are antichrist. Concerning these he is admonished to be very careful and not to risk his spiritual stability by allowing himself to be deceived.

The Apostle John wrote: "Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he has both the Father and the Son. If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed; for he that biddeth him God speed is partaking of his evil deeds." (2 John 9 - 11). This is the hard but the necessary course of action for one who would protect himself and his family from spiritual danger.

5. Be willing to contend for the faith. Scripture calls upon us to earnestly contend for the faith, which means of course to be willing to defend the truth of the Gospel in the face of satanic adversaries. (Jude 3). We have illustrations in Scripture that this sometimes means coming to a point of contention with family, friends and associates. The Apostle Paul was surely a beloved friend of the Apostle Peter, but he said, "When Peter was come to Antioch, I withstood him to the face, because he was to be blamed" (Galatians 2:11). In this case Peter was guilty of doctrinal error and was thereby cooperating with the Judaizers who were subverting the people of Galatia into heresy.

Indeed Jesus Christ Himself had on one occasion to turn to His beloved friend, also the Apostle Peter, and say, "Get thee behind Me, Satan" (Matthew 16:23). The true servant of Jesus Christ must be careful that his friendship with Jesus Christ is the association that is absolute. By comparison to this, all human associations are relative.

The first principle of the universe is truth and this must be defended even at the cost of our lives. Surely the Apostle Paul was serious when he named us all as soldiers of the cross and gave us a detailed list of the amour that we should wear in order to function properly as contenders for the faith. (Ephesians 6:10-20).

Our spiritual sentiments, and this is the most sentimental age in the history of the Church, would lead us many times to feel that contention for the faith of the Gospel is somehow unspiritual or undignified. Nothing could be farther from the truth. The analogy of the Christian being a soldier of the cross in a world that is described as a battleground, is repeated many times in Holy Scripture.

The essential struggle is the struggle between truth and untruth

(from Know the Marks of Cults - the 12 basic errors of false religions by Dave Breese)