Awesome. XD
You have to put the URL of the picture in. For example if I wanted to your's in your signature, I'd use this URL (Unless you changed your signature sometime soon as the database or wherever would change the URL.)
http://www.pokecommunity.com/signaturepics/sigpic112103_29.gif then transform it into [URL]http://www.pokecommunity.com/signaturepics/sigpic112103_29.gif[/ URL] (No space) That should work for you.
All right, thanks. You?