I looked a bit into
https://bitcointalk.org/index.php?topic=1633458.0 and found that you cannot create a post, preview or change signature to with code containing:
7 closing color tags
6 closing center tags
7 closing font tags and a closing url tag.
combinations of these (4 closing color, 3 closing font, 1 closing url)
and probably many more.
in
any part of the text, even if it is enclosed in [nobbc] or [code] and has proper opening tags. (pair of tags opening and closing immediately is not counted. /center, /center, center, /center, /center, /center, /center makes only 5.)