In the reference implementation there's a file called (in my extension anyway) gdnetreplysign_overlay.xul which has this line:
... an overt Ghost Busters reference, which should remind developers that "xul" is pronounced "zool". [wink]
So anyway this extension I did adds a couple of extra buttons to pages that allow me to sign using (currently hardcoded) html to put my image banner optionally at the end of posts. I'm going to try it out over the next few days and with any luck it won't upset anyone and I can use that banner I made on Sunday.
In the GDNet chatroom I now sometimes go in to at home (via Gaim at the momement) there were those whom would want signatures to go altogether. Also those whom think images as / in signatures isn't a good idea. Now as I had to code around my own extension to sign using an image I guess it's discouraged, but I have checked around and cannot see anywhere that it is banned.
Personally I think my signature is pretty tasteful and takes up the equivalent to 2 or 3 line of text, so I can't see anyone having a problem with it. But as with everything else we shall see.
I've given (and will give out) ratings to anyone whom does this welcome wagon thing of leaving a note on my journal.