I will keep it brief. First off the positive, you have a knack for text. Just wanted to let you know that. You do a great job of finding fonts that match your sigs and placing the text well. That said, I see one negative on each sig.
1. I would try to get away a little bit from the glow layer style on the renders. Experiement with some other ways of getting lighting on the reders and drawing attention to the renders. Some white brushes set to overlay can do a great job of that behind the render as well as some light brushing on top of the render.
2. The only thing about this one is how dark it is. I would try to brighten it up if possible. How, I am not quite sure, but I would play with it a little bit or just keep it in mind for the future. Maybe play with some adjustment layers. If you haven't used them, PM me and I will see if I can give you a couple tips on them.
Yeah them being too dark is really something I'm struggling with. It seems like when I try to make them lighter that they either appear too washed out or the renders look funky. I'll follow your pointers in the future. Thanks fellas.