How about signatures that have overtly religious or political content? Not spam, but can be a little obnoxious to those of different viewpoints.
I think religous and political diversness is the perfect way to keep us from becomming droids, and insures diversity. I have no time for those that would impose their views on me just because they dont like mine. Your beliefs are yours, and mine are mine, if you dont like mine, block my posts, and I'll keep an open mind.