In the Manager User Groups you should be able to deceide which group can use a signature or avatar it would be handy if you wanted your boards to load faster.

Also this would be useful to me because I am a Game Admin. and use IPB and I don't want some member groups to have signatures.

Avatar disability is already an option. As far back as 2.0 if not earlier.

Not signatures

If there is no effect, you can disable editing of profile information. Once the user registers (and set it) it remains that way forever. I could have sworn there is a way to restrict signatures.