Some used one big banner for a signature. As it was said by DabsPoorVersion above, he tried and found that you can use not more that one picture for a signature. But it can help anyway if a designer will keep in mind a possibility of using it in signature overall design.
I think they can make one big image and add additional links below with the same way like it is used now.
Signature designers should test signatures in all browsers before they release it for altcoinstalks forum to make sure everything is working fine.
You can even have an animated pic in the signatures, although I don't like having a lot of animation in the signatures.
Adding pictures with words in the signature usually gives bad results, so whoever wants to design a signature with an image is better to do it from scratch.
I didnt know that, but I think we already have some animations in current signatures here, for example Unijoin.