I like the concept but it doesn't look like you've done much I'm afraid. Looks to me like a graffiti background clipped on to downloaded brushes =o. I know I'm worse than you with downloaded stuff lol. But apart from that, try to space out your vectors because you cant really see what some of them are as the bg is the same. Add a light source pl0x, although the render had alot of depth to it already! In the end the sig does look nice and there's not much more you can do to improve it without changing the style of the piece.
7/10