Something in the code of the website apparently. It's fully randomized at this point how many characters you sig can be. So some people can do a sig just fine, some people (like me) have a limit of 4 characters that INCLUDES the characters from a URL. So essentially we can't have one.
Given it's an issue with the code of the website, I think they've deemed it as a super low priority for now. I can agree with that. If it was a fast fix it should be done already but it doesn't sound like it is. Sounds like they will have to pour through code for hours to find that one unclosed tag or something.