I've noticed a lot of theories regarding why there was a space in "LA X," and I think the most simple explanation is that "LA X" denotes that we are in Los Angeles in a different timeline ("Timeline X" or "Reality X" or "Dimension X," whatever you want to call it).
"X" just denotes that we are talking about the "flash-sideways"/alt-reality characters.
For example: Jack is in the Temple wit the others, but Jack X is waiting to find out where his father's coffin is.
See? It's easy!
Sayid just came back from the dead, but Sayid X is on his way to (hopefully) find Nadia.
By adding "X" to the end of people's names, we can easily denote who we are talking about in which timeline.
TPTB were trying to help us out!