Yeah I definitely have no clue, and before even making a signature I even looked to see if there were restrictions, and found NONE. So if there ARE rules here, they need to be a lot more obvious.

EDIT: Oh and to who said something about having smaller images for those on dial-up?? Well there IS an option in your profile to turn off images and/or signatures, or both, so that will help out those on dialup. Instead of an image there will just be a a link to the image instead of the actual image. So I don't think size or loading time should really be that big of an issue since you can turn images off.