Chris, you want your signature to be a scene. The starfield is a good start because it's a fitting background, but your render has a white light coming form the top-right, but the light source in your sig is behind him and it's red.
Great work on the background, but it seems the way the texture of the planet is applied onto the sphere is weird. It seems there's a lot of lines going like this:
You need to have an idea of what would be reflected, draw it in black and white, reshape it so it fits the perspective, set to color dodge, lower the brightness so that it looks good, then alpha-mask the reflections that don't land on the star.
To get the perfect selection, select the transparent area with the magic wand, fill in the selection on another layer; run Gaussian blur (~5px radius), and use the magic wand's tolerance to have an optimal selection, as opposed to relying on hit and miss.
The perspective is off, you should be seeing more of the upper face of the cylinder for the pawn.
Also, that font isn't working with the sig, just go with all caps Arial in size 20.
Nice concept, by the way
No, at least not on dA. The thumbnails get messed up if they have a transparent background, and besides it's a logo, the background it's on at the moment doesn't matter.