I'm sure I'll be quickly corrected if I'm wrong, but I think the rule is that links to commercial sites can only be listed from the Home Page URL spot in your user profile (i.e. no direct link to a commerical site from a post).
I am looking for a solution that will allow us to bring the image tag back in signatures. I want to automate the size enforcement of footer images just like avatars. Maybe this will come out in the next release of the forum software.