The lack of sig lines doesn't much bother me. I enjoyed some folks' and used them as quick links to find parts of the wiki that like to play hide and seek. The ones for vendors were rather nice. There are other forums that I peruse that annoy me greatly with huge walls o' sigs (video game avatars back when I used to be a dork and play WoW, etc).
I don't claim to be a code type person beyond some basic HTML I learned about a decade ago so I don't know if the forum software allows it or if it does but it requires too much out of our mods but my suggestion for the vendors is to have the little blue button that says "Vendor" above their avatar actually be a link to the vendor thread or website that pertains to them? You could even charge a fee for for a link that goes external vs. one that just links to the vendor thread here.
I'm sure that if it is possible the logistics of doing it to an external site and having folks pay for it might be challenging, but it could turn out as a decent way for the forum to get more advertising dollars to cover costs and help some of the smaller vendors who can't yet afford one of the regular banner ads.