Thanks for pointing this out, it has been fixed. It looks like some signatures are now broken, I did a quick investigation and it appears the BBCode wasn't valid inside of them in the first place. Previously we would automatically fix code in signatures if it was wrong, we won't be doing that going forward.
Make sure you close BBCode tags, like:
color
And you can no longer use HTML div tags (that should not have worked previously)
<div>
I've increased the character limit in signatures to accommodate this change. If anything else appears to be broken post in here and I'll get it fixed. I'll be making a topic sometime this weekend going over the new improvements to the forums.