Some of the avatar and signature restrictions have changed from the old board - changes are bolded:

Avatars may be uploaded from your computer or from another website, or linked to from another website. No longer do you have to host your avatar elsewhere!

Avatar size must be at least 20x20 pixels and no more than 200x200 pixels. This applies to both uploaded and hosted avatars.

Uploaded avatars may not be more than 10,000 bytes in size; linked avatars hosted elsewhere have no file-size restrictions.

Signatures may be a maximum of 255 characters and may contain smileys and images, and up to five links to other sites (such as band pages). Images in signatures may be no larger than 600 pixels wide by 100 pixels high.