Well, in fact it tells other people a bit about you. Of course you could do the same with another form of signature. And I don't like people having 50 "cola-cola" / "mtv" userbars in their signature, thats just useless and annoying.
However, as i'm a Retro Gamer, I like people in Forums who use, for example, a "Sega Saturn" Userbar. You direclty know what they like to collect/play and stuff.
Its only useful in smaller communities I guess. When you are new and dont know everyone that good.