Not sure how to implement this but a forum I was on would automatically hide parts of a sig if it was over x amount. Your signature would still be there but it would only display the top of your sig (if that makes sense, I don't have a screenshot anymore of it)
Basically I once had a sig on this site that was just about 3 pxs over and the bottoms of letters like g and y were cut off. Yeah this sounds confusing to me, does it make sense to you guys? And the full signature would be displayed on the user's profile "About Me" page.