I would suggest you to stop using brushes. You could use stocks instead, they look and fit much better then just brushing on your signature. Your signatures don't have much flow, lighting or depth either, no offense. I would suggest trying to blur the parts that seem sharp to you with the blur tool, to create depth. For flow, see where your render/stock is moving, and try to build from that. As for lighting, add lighting where the original lighting in the stock/render was with a nice soft brush.
I agree with cycangfx, even tho i think the 3rd one would look pretty good with a smaller render and some depth, and the 4th one isn't too bad
