The sig is very dark and has poor contrast. Next I would add a light source. If you don't know how to do so there are a few ways it can be done. The easiest way is to go to get a soft basic brush and make a large dot where the light should be coming from, then change the layer options to soft light. You can use the burn tool to make shadows to improve contrast.
To blend your render try to use the smudge and the blur tool. Play around with Cd4 renders and look up so tuts.
For your sig I will rate it 5/10 for the effort! Keep trying.
