I don't think there is a post requirement for signatures, but there is for posting links. As for a BB sig. bar, I don't know one off hand. Actually, haven't seen sig. bars in many years now.
On another forum, I have at the bottom of each post a window about this size..
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and in it is a picture of an American flag with the words God Bless America.
For this site I'v been looking for one that says Blackberry yada yada.
Well, you can post whatever you want in the sig, some people have images, Ive seen a flash video...thing.. regular sigs, quotes, links to popular questions around CB etc
I forget who it is, but there are members who will make a lil wallpaper thing, some make other members avatars etc..
perhaps post a question of what you need on the discussion board and someone may come thru for you.
Some people keep the link to their hosted image copied to their memopad, then right before logging in to CB.com they copy it to their clipboard and just paste it to the end of every post making it seem like its part of their sig.