If you are trying to post a gif as your avatar, it may be somewhat difficult because the file size limit for avatars are 19KB, I believe. Sometimes, even if you use an online image compressor like shrinkpics (http://www.shrinkpictures.com
) or Picasion (http://www.picasion.com
) where you can customize the gif that doesn't exceed the dimension limit, (100px wide and 100px high) the resulting image may still exceed the 19KB size limit. You actually have to find the perfect sized gif to pull one off as your avy.
As far as your signature, if you are trying to post a gif there, you just have to make sure the image does not exceed the the dimension limits which I believe are 400px wide and 300px high.
Hoped that helped man, good luck.