Agree with, show support. Usually used on forums, such as WoW and preceeded with / to represent in-game emotes.
Comes from the signing of petitions to support an change or idea.
-A word proceeding your name at the end of a written work, such as a letter to someone.
-A way of expressing agreement or approval of something, used much like word, hell yeah or I concur.
Leo, Andy's been raiding the fridge again.
P.S. You're da man.
"Man, guys! Paula's SO HOT!"