What I don't like about signatures is that you see them over and over, and they can prejudice you against a person very easily. If I'm talking to someone about Snape and we have similar views, I can like them - and when I find out they think R/Hr is really stupid and boring, I don't care as much because I already liked them. But if they have a sig that proclaims how much they hate something I like, I probably won't bother. I like how on LJ you can't tell someone's opinions before they say them (in comments, I mean) unless they have a really telling icon.