It might be useful to discuss exactly which restrictions on signatures are worthwhile and which are not. For me, the biggies are:
- disallowing sigs to members below a certain post count
- limiting font size
- limiting number and size of images, and perhaps disabling images altogether (preferably by usergroup)
- limiting number of links, perhaps disabling links altogether (preferably by usergroup)
- limiting size of signature by number of lines (I don't like character limits)