This is good. I looks like you have some general knowledge of photoshop. Though i think we need to finesse your skills.
The first and last are the best.
1st sig - the coloring is pretty nice. Also the background is looking pretty sleek, however it looks a bit filtered, which we don't want. So try and ease up on the filtering.
When making backgrounds depending on the render i usually either smudge the render so it covers to whole background and then lighten the opacity of the smudge.
Or I blur the render so it covers the whole thing, and then lighten the opacity.
Both of these approaches seem to work very well for me and others. I'm sure others will tell you how they do they're BG's(backgrounds) too.
I think you need to blend it a bit better. the render is just kind of sitting on top of the BG, usually I overlap some smudging over my render, or i put clipping masks over it. it's kind of a personal preference but next sig i want you to really try to blending your render in more :P.
With text you should try to remember to use default fonts and to try and make them blend. I would read DarkMethod's guide to text. Check it out Here
It's pretty helpful and if you read it you will master text a lot faster than you would just shooting in the dark.
Overall the sigs are okay but they need some work.
:)