Sure I'll design you one... It'll be in my freebies sometime tomorrow!

Just kidding. You realize that someone could very easily remove that signature in photoshop right? Anyway, Take a look around at some art other than what is posted in the Renderosity galleries in any medium and observe the proliferation of big signatures! Notice the scale of Monkeycloud's signature also.

Critique is simply a part of any "normal" artistic dialogue... my only other advice is to say it's not the graphic quality of your sig, it's the scale in relation to your art. I really liked your render for the challenge otherwise. Very well thought out and executed, plus I enjoy detailed imagery.

:)