Hangman!

manuelgv said:
Ok so does it have a P and H?

NOPE, no O L D E R Y U K P H and 2 guesses
And a great big hint!!!!!! 6 6 6 six six six Greek 666!!!!!!
Like in the Bible, you know 'mark of the beast' :)

_ H I - _ I - S T I G M A
 
Chi Xi Stigma

(although I still think it's Sigma, because the other two are greek letters too)
Edit: Ok, it bugged me and I searched for it. It appears the greek letter "digamma" is called stigma sometimes, so gatedropper is right.

But I looked it up from google, after the hint. Someone else go... I'll be away for the weekend anyway.