How to stop cross linking of attachments within forum?

[Sweet Cheeks]

I searched around the hacks dbase and could only find hacks that prevented hotlinking from outside the site. Perhaps I missed one, but what I am looking for is a hack to prevent cross linking from within the forums?

My problem is users are posting a "test" thread in our tech forum, then linking to that attachment and using it in their sigs aranoid: Any ideas on how to take care of this?

Thanks for your help