Ah, I don't know man. I have been a part of many of these gaming forums, and sure, some people abuse it with obnoxiously themed (or sized) signatures, etc...
But, overall, I think they allow us to put forth a bit of "personality" in this otherwise sterile internet environment. this forum, for example, feels a bit plain and personality-less, for lack of a better word.
For example, Mike, even the quickly set up forum for our Meta campaign (I am over there too), allows for avatars and sigs, and is leaps ahead in that regard.
Just my 2 pfenigs.