I do not use images in my sig, but I can see why people do.

tF's main reason for this is slower loading times. So why not get rid of avatars as well? They use more bandwidth than sig's do, as most people have avatars and not everyone uses images in their signatures.

Like others pointed out above, if you are on 56k or just have a slow connection, then turn signatures off in the UserCP!

Considering that this is a design forum, people should be encouraged to show their talents and like Salathe stated above, it compresses a 5 line speech into a 200x100 image. An image speaks a thousand words!