Usually used in message boards to denote that the statement you have just posted has a sarcastic tone. Comes from HTML code.
Wow, you are the best because you have a high post count./sarcasm
Yes, because you're the only one who knows how this shit works, aren't you /sarcasm
It means you're ending what you said sarcastically.
Jeffree Star is obviously the most gorgeous woman ever. /sarcasm
Jeffree Star is obviously the most gorgeous woman ever. -end sarcasm-