See the link below - there's no reason to at least not try.
These things are truly annoying, not to mention people that have them as signatures are uniformly neither reasonable nor smart (see PC Audio forum).
It's not retroactive, of course, so you would have to come up with an approach of forcing users to re-upload the images. That shouldn't be that difficult though.
Edits: 10/17/14This post is made possible by the generous support of people like you and our sponsors:
Topic - Disabling animated GIFs server-side - carcass93 09:44:23 10/17/14 (0)