The three letters in Greek used in the first image is also the Arabic letters that spell the Islamic moon god Allah.χ is a lowercase letter and is the Greek letter Chi which is valued at 40. Already, we can see that a lot of people claiming the belief that it's 666 is a fallacy. The second letter is ξ which is also lowercase and it's value is 60. This second letter is called Xi. Lastly, we have ς which is also a lowercase letter and it's value is 200 and it is called Stigma. The value being 300 or rather, the lone number 3 as zeros (0) are not counted.

However, you may have seen in the news in about the year 2006 that a fragment of the "oldest NT manuscript" was found to say in Revelation 13:18 that the number of the beast was 616 instead of 666.

The report of this finding is thus:
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A newly discovered fragment of the oldest surviving copy of the New Testament indicates that, as far as the Antichrist goes, theologians, scholars, heavy metal groups, and television evangelists have got the wrong number. Instead of 666, it's actually the far less ominous 616.

The new fragment from the Book of Revelation, written in ancient Greek and dating from the late third century, is part of a hoard of previously unintelligible manuscripts discovered in historic dumps outside Oxyrhynchus in Egypt. Now a team of expert classicists, using new photographic techniques, are finally deciphering the original writing.

Professor David Parker, Professor of New Testament Textual Criticism and Paleography at the University of Birmingham, thinks that 616, although less memorable than 666, is the original. He said: "This is an example of gematria, where numbers are based on the numerical values of letters in people's names. Early Christians would use numbers to hide the identity of people who they were attacking: 616 refers to the Emperor Caligula."

The Book of Revelation is traditionally considered to be written by John, a disciple of Jesus; it identifies 666 as the mark of the Antichrist. In America, the fundamentalist Christian right often use the number in sermons about the coming Apocalypse.

They and satanists responded coolly to the new "Revelation". Peter Gilmore, High Priest of the Church of Satan, based in New York, said: "By using 666 we're using something that the Christians fear. Mind you, if they do switch to 616 being the number of the beast then we'll start using that."
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But I personally do not agree with either as we must remember that even though the Romans were ruling at that time, the Jews still read and wrote Aramaic and Hebrew. In Jewish culture, it is considered that something that is in the mind is your thoughts, and something that is in your hand or on your hand is an action.

Also remember that the Revelation passage states,
Rev 13:17  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. 
Rev 13:18  Here is wisdom. Let him that has understanding calculate the number of the beast: for it is the number of a man; and his number is χξς. 

Firstly, the three types listed above are as follows:
1. The mark
2. The name
3. The number

Secondly, we have already looked into what the three Greek letters represent using the Ancient Greek letters. These would have been the letters used and in common existence back when the disciples were writing their books and even when Yochannon (John) himself was writing the book of Revelation.