"And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads: And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name. Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six." Revelations, 13:16-18, KJV translation
Scholars have been scratching their heads about this passage of revelations for centuries, wondering what the significance of 666 is. Is it an anagram? I've seen many attempts to assign numerical values to letters to come up with a "count" for a word that means the beast, which is silly, because the ones I've seen are in English - a language that wouldn't exist for 1500 years after St. John penned this passage on the Island of Patmos. Some have used gematria - a form of Jewish numerology that assigns numerical value to Hebrew letters and words - to try to tease out a hidden meaning of the number, but gematria doesn't appear anywhere else in the New Testament.
I recall a comedy about the apocalypse named "668 - the Neighbor of the Beast." Nice to have fun with this stuff.
More people focus on the mark on the forehead or the hand, and ignore the significance of the number itself. They panic when they hear of ideas to implant RFID in people's hands for easy recognition - "The mark of the Beast! Noooo!" While I'm ambivalent about the idea, I can see some utility, and I recognize that our current preoccupation with personal privacy is a relatively recent development in human society. Throughout most of history, you were well known within your community and were deemed suspicious if people didn't know you personally, including your history and social standing. No, such an idea is not a harbinger of the beast.
To really understand the Number of the Beast, you have to look at the context. St. John was given revelation in the form of visions, and he faithfully recorded what he saw, even if he didn't quite understand it at the time. He was allowed to see future events, but it wasn't always explained to him.
Let's look for a second at the original Greek that Revelations were written in:
ωδε η σοφια εστιν ο εχων τον νουν ψηφισατω τον αριθμον του θηριου αριθμος γαρ ανθρωπου εστιν και ο αριθμος αυτου χξς
-Revelations 13:18.
I've highlighted the "666" in red. The written Greek language had no numbers. They used letters to represent certain numerical values. Below is the table of the Greek numbering system.
So we see that St. John wrote "chi - xi - stigma." These letters mean nothing in Greek by themselves, so it must be a reference to a number, and that's confirmed by the context where St. John refers to it as a number. Subsequent translations have rendered it as 666.
Was St. John really referring to a number, or just recording what he saw, and his own interpretation? People from all walks of life receive the mark, and without it, they are not allowed to function in society. What is the mark? "chi - xi - stigma." Three Greek letters. Is it an anagram? If it is, is it in Greek? Is there anything else that can be confused for these letters?
It turns out there is. In a language whose written form would not be recorded for another 600 years from St. John's time, which reads from right to left, instead of left to right as Greek does.
In Arabic, the words "Bismallah" ("In the name of Allah!") followed by the crossed swords of Islam (remember, Arabic reads right to left) bear a striking resemblance to the Greek letters "chi - xi - stigma."
Did St. John see a vision of the Jihadist movement, where everyone wears a green bandanna on their head or arm ("hand"), indicating their allegiance to Allah and the Quran and chanting death to infidels? Not understanding the Arabic writing (How could he?), he recorded what he saw, and decided it was a number, for it couldn't be anything else.
Anyone who has studied the Quran from the frame of reference of Christianity understands its Satanic origin. It teaches many doctrines of the Anti-Christ, not the least of which is the denial that Jesus was ever crucified. We know the Beast is the Anti-Christ. We know the overt, stated goal of Islam is world domination, and the subjugation of all peoples under Islam.
So don't panic when you see people getting RFID chips or invisible barcode tattoos. As questionable as those sound to liberty and privacy minded modern people, they're not the mark of Satan or the Beast. The Beast is Islam, and St. John overtly told us what to look for, even if he didn't have the frame of reference to understand what he saw at the time.