try and use the dodge/burn tool too darken the bottom of the signature and use a soft brush for the light source on the top of the signature....
also i think, im not sure but i think your using a stock for the background, if so grab your render and smudge it and create a background with it then smudge it again and set it in dodge then add your stock on soft light mode it will look much better i have a tut on it in gimp but you can translate it into PS just look at my posts