I always thought it was some crazy, warped version of "lol," possibly originating in the anime fandom since I think they came up with all the crazy little eyeball emoticons. But, it's supposed to look like a little person cheering, completel with pom-poms, right? Right? *does a little dance*
Part II: While I'm having Revelation Day, I also finally figured out which Winchester was Sam and which was Dean. AND which was Jared Padelecki and which was...oh, what's his name...Jensen Ackles? Yes. Now, my task is to keep these facts straight in my head so I will stop being horribly confused when people on my flist start flailing about one of them.
Dean = Jensen = the guy from Dark Angel. The guy you always confuse with the bug-eyed guy on Prison Break. The snobby-looking one whose character you hated on Dark Angel. Ackles raises your hackles. There we go!
Sam = Jared = puppy dog boy. The younger-looking and cuter one (though that's not saying much). Remember that 'Jared Padalecki' is more fun to say, so it goes with the cuter one, and also that Sam is more likely to be a dog's name than Dean. Voila!