You should try and broaden your work by making artwork that is at least of 1024x768 size and later shrink / cut out the parts you want made into a signature. You can achieve a much greater realism when you're not stuck to the 500x100 size limit our forums use. If you aren't too offended by criticism as many others are -
You have no visible focal point which makes the image very flat, cutout design or not. The biggest mistake most people do when it comes to blending is they think just because the background is blue the entire render / stock / 3d import has to match this color, but it doesn't. To blend is to make the entire image seamless and most importantly make the lighting match.
Theoretically if only your background has a light source then the imported model should be completely black or at least very dark, depending on how strong the light source is, adding some source of light on top of the model is almost a must if you're looking to add some level of realism.
An example would be this image:
If you had copied some of the fractal artwork (the background light "beams") on top of the model you would achieve an entirely different depth.
Same with this one, if you take one of the bigger light particles and put it on top of the model, possibly even with a lower transparency it would look more part of the background.
All of this mentioned is quite hard to achieve when you're working with something as small as signatures, but small touches can make a huge difference towards the end. This is the reason I stopped working with small images, the level of creativity and detail you can put in is very limited. I still get requests every now and then, and when I do them I simply make a large piece and scale it down while cropping out the most important parts. Works just fine.
Good luck.