Why do WoW gamers post on unrelated message boards?

I've noticed on more than one message board that sometimes, a new user will register and post a bunch of completely irrelevant, often nonsensical posts on several different threads, sometimes bumping a very stale thread to the top for no reason. The signature will contain references to the game World of Warcraft, but since I don't play, I don't know what people gain by this. Does the game somehow award points for this? Or are the spammers soliciting customers for some type of online business?