I am still learning to make sigs or with graphics period. I thought i would post some i made and ask you guys/gals for some tips/help/criticism. Most of these were made by me just experimenting with some things and the font isn't the best.
I'm not going to lie, your currents are much better than these three. The third one is probably the worst, no real background and a lower quality render with minimal blending. The second one needs more blending on the render, and that blue streak next to the render's elbow isn't working for me. Background could use more depth as well. I take back what I said though, the first one looks okay. I like the ice theme, and it goes well with the render. It's simple, but it's decently eye appealing. Again, more blending on the render though. Since you said you're just starting out, I'm going to give you a little advice, heed it or not, cause I'm not a GFX master, not by a long shot. Get away from the second and third posted ones and head more towards your current signatures. Try to get a little more depth in your background, you'll probably want to stick to brushes at first (find them here or on DA) but when you get more comfortable, you can use filters and smudging as well. Also, I would work on blending in your renders better. You can either smudge the edges, or use a soft brush eraser (my weapon of choice), or filters. I'm sure there are some great tuts about blending somewhere on the site, if you want examples. Text is always hard for me, and a lot of other people too, but for the most part, I find that default fonts or fonts that aren't that 'fancy' work best. Like the one in your brain freeze one works well for that one, but most of the time I would just stick to regular fonts. Each signature is unique though, so just experiment and see. Finally, if you really are just starting out, read tuts. They're really helpful and can teach you a lot of cool things. You don't have to follow them step by step, though you can, but simply learn from them and use different techniques to create your own style. Hope this was helpful.