Your sigs aren't bad. I can definetly see a lot progression as your sigs get newer and newer.

I would work on text. Stick to default windows fonts they tend to look better with all kinds of sigs. I like Eurose, Eurostile, and arial.

Your blending on the last few sigs are pretty good so i like that. Also work on your lighting. The lighting on the 5th sig from the bottom is pretty good. So i would recommend doing more like that.

Finally borders. Most of your borders are pretty good but try and stick with 1 px black or any borders like that. the 5th sig from the bottom's border isn't very good. With a sig like that i would try maybe cinema styled borders.

Anyways not bad sigs..I definetly see a progression so if you keep working i garuntee you'll get a lot better.