A Couple New Sigs

It's good you are using defaults but these defaults..look odd. Your text is def best in the first sig. You kept it simple and minimal, it looks nice and clean. In the other two the text is too big, too spread out and just in an odd font. I would also try to keep your text down to around 4 or 5 words max.

Overall your second two sigs have the best BG's however I'm not digging the duplicated render in the third sig.
You should try to work on blending though. it seems like you have a nice grasp on smudging so i would suggest overlapping some of your smudging onto the edges of the renders.

You might find it helpful to make your signature sizes smaller, when you are still learning it's a lot easier to make the sig look full when they are smaller rather than so large. I try to keep my sigs around 360 x 110, but i like mine really really thin and long. A more reasonable size is probabaly like 320 x 135.
Good borders though, and looks like you are getting the hang of it pretty quickly. You should def keep making more!