I hope my reviews don't seem too harsh.
1. Unfortunately to me this seems like two sigs cut and pasted together. It looks as if part of the (seemingly) main render was cut and then pasted in odd areas. The (seemingly, it's hard to tell) background on the right also looks as if it's been cut and pasted.
2. Follow Iron's advice. For a beginner sig it's pretty good (I've seen alot worse), but it's hard to tell exactly what you were aiming for. Try not to make your render's have such hard pixels. Sometimes hard pixels look good, but I think in your case it would've been better to have soft pixels that blended with your background. With a good graphics program and some decent brushes your lines could look pretty good. I suggest using the font tool instead of handwriting. Both have advantages of course, but most times it's easier and looks better to use the tool. Search
http://dafont.com for some good fonts.
3. Basic, but good. The render and BG fit well together and the lighting works. I might've rather had the text faded resting on one of her shoulders or put it in the bottom RH corner. I can't tell if you blurred a copy of the render or just used brushes for the right side but it fits well.
4. To me the white doesn't go, or maybe it's the green. I think a black or dark green border would've been better and a different render (perhaps on of the overly used Halo renders would work?). I think the text would work regardless of the intended color of the sig.
5. I just got a bad impression of this sig for some reason. I think I've seen the render before but I can't place where. To me it looks like a scaled up, blurred, version of the render is in the BG behind it.
6. *Quotes Iron Maiden* I'd just like to add that text is perfectly placed and stroked. The only thing I dislike is the two black columns along the sides. On a black BG they're invisible, but I think they should've just been left off. I'm not sure of the effect they'd have on a white forum though, perhaps they'd look alright there. I think it'd be better with a simple faded white 2 px border.