Avatars & Signatures
The rules are also applied to your avatar, signature and PM's, not only to your posts.
Also, in order to be eligible for a custom avatar and signature, you must've been registered for at least 3 months and have more than 125 posts.
The maximum size for images in signatures is 350 pixels in width and 250 pixels in height. If you put more images or text in your signature, then the sum of their width and height with the white space must not exceed 350x250 (including the white space between them). The pic is not allowed to be animated gif.