X refers to the sentence/context of the message you're replying to. (^) the direction of this symbol, will determend the direction of the message you're replying to. X^ means one message up to the right (usually your own message). ^^^^^X means 5 messages up to the left. This symbol can be displayed on it's own, usually this means that the person just wants you to look at this message, but it depends on the context of course.
X can be used in capital or not, you often don't even use X on It's own, but it can be used for directions if you don't have a/any sentence/context.
X^ and ^X or ^^^ are mostly used in chats for practical reasons:
The sacredcombination of boredom to be found by you, INSERT NAME HERE. If you found this, you started at the top row, held shift, and typed each key at the top In order from left to right 3 times each.
You: Try every combination! Find the unused combination!
Other man: I’ve found it! It is ~~~!!!@@@###$$$%%%^^^&&&***((()))___+++
You: No, because the person who wrote it found it first. You have to see the *NO DEFINITIONS*.