IF I may make a humble suggestion as a fellow artist. Try using more perspective, graffiti is flat and harder to grab someones attention without perspective. Detailed perspective especially. Try adding characters or othere themes to your graff. I have a monkey that goes with alot of mine. ALso colors, colors will stand up and grab your attention. NOt to say that I don't like this at all, but it leaves me wanting more. Shading, color, perspective, something else going on...I dunno something though.
SOrry if this seems douchey, if it does, then ignore it.