Marco DI LEO wrote:

> I'm not English-speaking but I guess X stand for 'cross' rather than
> 'trans'.

  Both observations are correct.  To "cross" is in latin, "trans" =
across.  In English for alliterative reasons, "Criss" is a variant of
"Cross" (to cross *again* is to "criss-cross") and "S" is used for
"Criss" or "Crys" or "Christ" as in the vulgar abuse of: "Xmas".

  "X" is used for a few other things too, derived from its algebraic use
as "the unknown quantity".  Title of a pseudo-sci-fi TV series:
"The X-Files".

  Cheers,
        Paul B.