It's like a secondary way for people to get to know who you are on the BBS, but more of an 'at a glance' way. I think a lot of people are trying to elicit a certain reaction from the public out of their signatures, whether it is a quick laugh, inspiration, awe, interest, amusement, or whatever else. Personally, I want to give people an impression of who I am, so I've basically always refused to sport a sig that I haven't personally created. I like my current one because I managed to fit in a bunch of the MSPaint imitation art I've created over the years, incorporated one of my favorite quotes, and included my name.
I don't really understand how you can claim that signatures 'get in the way'. Most of your posts are so small that the signature is just cutting into the empty space you guys feel the need to share with the forum.