What caught my attention on the roads in U.S. was a traffic sign with XING and a jumping deer, standing for 'deer crossing' and XINGPED announcing a pedestrian crossing place.
Obviously the cross part here is replaced by X.
But what about Christmas? Xmas. Here it replaces Christ for Christmas not Crossmas.

Anyone knows more specifics about this X- matter?
Are there more words where X takes over part of a word.
Crossfire? Xfire? Aren't there many with which you could do the same thing? Or has this crossed the topics before?