Their not very good from a graphical point of view, looks like you haven't been with graphics for very long. I see potential in your second signature, you just need to get better with blending, unless that was the style you were going for. I would have either done a clipping mask of a red gradient on the background or a blue gradient over the car.
Depth is pretty good here, but.. the lighting on the car doesn't fit, you didn't have a light source so you should have burned the car a bit with the "burn tool."
The renders could be worked on some more, to blend in as a whole signature. The blue text on the kirby signature should have a closer color to the general pink color scheme.