Yeah, bring back the double line. Maybe, this may be too much work, allow a switch for those who want, to have their account only display all sigs as different from the forum standard, say a different color background. I realize the programmatic problems with this, but it always seemed to me the board should warn of overly long sigs, or even not accept them (the calculation to determine this would be tricky). On another board I'm on, phpBB, sigs can be any length; people don't abuse it though.
Another thing related though, if I have a signature, I like a default amount of space after my post's text and the signature, and the sig, and also between first line of text and top of post; currently I just add bold tags with the requisite blank lines between them, but it seems bothersome to have to manually do this for every post. (And I think, not sure, when people quote me in replies, without editing the quote, this ends up with unnecessary blank lines in their reply.)