I have "Don't allow images in signatures" enabled, however a newly registered user was able to place an image in his signature by using the image ubbcode tag...
His signature is:
[image]http://i26.photobucket.com/albums/c111/crappypunkguy25/672851254_l.gif[/image]
And I have the option enabled not to allow images in signatures:
CP -> Master Settings -> Feature Settings -> "Allow [img] tag in signatures?".
IMO the "[image]" tag should also be included...