Show/Hide Signature based on custom profile field
 

I have a custom profile field that is a yes or no question. If yes, hide their signature, if no, show their signature. In specific forums only.

I've seen this in another forum using vBulletin, but I cannot figure out how they did it. They do this for both signatures and avatars.

You need to put a condition around the avatar and signature in the postbit (or postbit_legacy, which ever you are using) using that custom profile field - probably $post[fieldx].