As per members' requests, we've added Images in Signatures as an additional perk to Premium / Folding / SETI members. It involved some hacking of the vB code, and the solution might not be very obvious, but here is how it works:

In the User CP, under "Edit Profile" you will find an option called "Signature Image". If you enter the URL of an image there, it's going to appear right above your text signature. It still requires non-empty text signature to have the option to add signatures to posts at all.

Note that it will only work for Premium / Distributed Computing members that have signed up as per these instructions:

Premium members have the option of using their SG hosting space to host signature images as well.

We reserve the right to disable this feature if abused by members.

Enjoy !

Edit: I'm working on another feature for Folding members that will allow for dynamic auto-updating images in signatures that show their folding scores...

Here is the "beta" version of sig images (find your name if you're in the SG Team and use it as a signature image wherever you want):