I was wondering if it was possible to make a hack that only allows certain user groups to use Images in thier sigs. I know there is one for vb 3.0.x but haven't seen it pop up for vb 3.5 yet.

admincp >usergroup manager

then edit he usergroups am nearlly possitive its a dafult in vb it shuld say something like allow user to use img tag in signature or allow user to have a signature

Just looked, only see allow users to use sigs. Don't see anything about img. Anyone else?

Is this possible?

Not possible with a default vbb3.5, however, you can limit the entire use of signaturs to certain usergroups, but I guess this is a bit to strict for you?