i really like this =], it may be plain but who says a sig has to be complex? The right side is a little plain, i would suggest text, but i wouldnt want it to be spoiled =P. Anyways i like it so kiu dai =] =].
As you said, bit dark and plain, maybe make the light source a bit stronger, and add a few more effects, but I like the whole concept and the text is great.