"Xmas" became the first shorthand of this kind because shop owners found it difficult to fit the whole word in the signs painted on their shop windows (back in the day when most stores were small, and there were no shopping malls, and advertisements were painted by hand on the inside surface of windows in cheap tempera paints, which could be washed off easily.) The X is a criss-cross. And so it stands in for Christ or cross, depending on what you need to convey. The use of the internet and now, especially, texting via cell phone and the limits on the number of characters in a Twitter tweet, has sped up the use of X for any use of Christ or christ. My friend Christine has always been Xine online. I know two other women online who call themselves Xtina and The Xtina. My cousin Christopher is X24 (Chris-two-four, i.e., Christopher). XIAN is a popular license plate prefix for some Christians. With the recent fashion in using "extreme" for everything from sports, to fashion, to spicy potato chips, we're seeing a lot more use of the spelling "X-Treme." All of these factors probably play into why Aguilera, an artist keenly aware of her image and who is in a business where being up-to-date is very important, doesn't mind being called X-Tina.
