I noticed some of your sigs are more of a square shape instead of a rectangle. That can be cool and all, But I think the rectangle ones look better because the images don't look so squashed in there. you have more room to work with and add text.
Try working with more fonts. Some fonts you use don't really fit your images. And Try blending the fonts. I am not that good at. But it does make a sig look better.
Also just adding an image with some words doesn't make a great looking sig. I really recommend you try out some brushing. Or working with renders and brushes. I think its better then a solid image and brushing on top. You can layer better with Renders IMO.
I am not trying to criticize you, just help ya out.
ok some more tinkering with brushes:
#6
I tried to bring out the blue in the headphones in the background while bringing out the red coat in the patterns. Also got the hang of smuging the edges to blend the image and the background better and used shadows to bring everything out more to break the 2D look.