Images are disabled for use in signatures on here and that setting cannot be changed.
There was a discussion about it a while ago but i cant find it now.
The only images that did used to work were the CTRA bars, but as CTRA has now gone they are also gone.
Some people still have the code displayed as their sig, but nothing else, but as there is nothing to link to anymore, all that shows is something like
[CTRA]---- lots of random code----- [/CTRA]
Doesnt really matter to me personally, as i go on other boards that have images in sigs fully enabled so people tend to add the biggest res picture they can, and they just get in the way i find.