all your renders are alittle choppy to be honest.
sig #1: The orange background shatters and blue render looks weird and the headshot you should fix. If you got that render out yourself normally i use the magic wand, magic lasso, and good ol' eraser.
Sig #2 the computer icons are alittle choppy and are really vibrant, plus the guy on the left is too dark, blends in too much with the background
sig #3 the render's fire looks alittle weird.
To make all these signatures look better i would suggest getting a good render before making the signature, put some sort of design/texture in the background (it makes the render pop more, and you can improve on your fonts. Download some fonts and add it to your C:dows/fonts folder and restart photoshop, that's what i'm guessing you're using. If you're using the portable, you need to extract the files onto where ever and not leave it in a rar document
All in all you did a good job, if you ever need help with anything i'm on msn or just pm me. Nice work, keep it up! My first sigs were terrible
If you ever need me to extract a render, or sharpen it up ask me, i love doing that.