So, I have some URL in my signature and attempted to change it, but it said "URL code not allowed". Is that because I'm no longer a Silver Subscriber or is URL just not allowed in signatures anymore and my current one only works because it's "grandfathered in"?
The latter - links in signatures are a subscriber function. But, it would be unfair and kind of mean to take away those already existing. So, as long as you don't change them, those links will stay put.