If you go into the settings menu and highlight the link in the sig box, then click the little icon of the tree at the bottom of the sig box. This should bring it up. you want the IMG code in brackets before and after the url link.
ie: {img]url link[/img] except the first character should be a bracket. I had to do it that way for it to show up.
P.S. I just tried it under my user account, using your url and it came up with you sig picture.