Quick run through...
Try adding some gradient maps to your signature to make both the render and signature blend in more.
First go to layer>layer style>gradient overlay (choose two colours from your render)
once you have done that add the render into the signature then mess around with the gradient maps. Go to image > apply image > image > adjustments > gradient map > choose one of the gradient maps and set them to either lighten, overlay, soft light etc.
Just mess around with that and you should be able to come up with a better background. Or you could always try adding in some stock photos as your background and set them to lighten with a gradient overlay underneath that layer.