As far as signatures are concerned, the less graphics the better. I'm on broadband now but it wasn't too long ago that I was using a 14.4 modem. Back then, just one graphic would slow the page loading time so much that I'd just give up. If you got 2 or 3 guys adding graphics, forget it.
I don't mind small graphic pics.... but in the long run, they're kinda a pain in the arse. All it means is you have to scroll more and keep looking at the same picture from the same guy every day.
Personally I prefer sigs with a simple link at the bottom like mine. Plain and simple and with a very easy to understand message.