I've always disliked animated images placed in avatars and signatures on forums because they are overly distracting. If such distractions are going to be allowed on forums, I usually wind up disabling them altogether in the User Control Panel so that they are no longer a problem.
I dislike images in signatures (or brightly coloured/long text) altogether and generally turn them off on forums that have the option.
I like Avatar images since they're out of the way and make it easy to recognise who's posting, animated or vulgar ones are annoying though.
I do like the way some people have made their signatures use light coloured text, maybe that should be made the default colour?