really solid for first sigs. looks like you have a lot of the basics down already. i see your biggest weakness at this point is the text, color wise and font wise.
the second johnson sig is the better of the two...but its too empty behind the left side of the render. if you know what stock photos are (pretty much any abstract photo)...try blending one of those into the BG...it will set the sigs off.
About the text, I really don't know how to get good texts from GIMP. The text options are really basic and I'm really stuck there. Also, I'll see If I can get a stock photo in there, I'll post an updated version of the sig soon.
I put in a stock photo. here's the new version:
wasn't 100% on that one, so here's another: