Some boards offer the option to not have signatures show up in posts. Not sure if that is a feature that vBulletin has, but may be worth exploring.
I for one would contribute, if it's an add-on to the board that needs to be purchased.
As an aside, if you use Firefox they have a plugin called AdBlock that can not only block ads, but images and avatars as well. Totally customizable and comes in handy!!