First thing wrong with this is, it isn't a sig, nor is it a avatar. Next, it is overly simplistic in the nature of brush work, and those brush splotches in the middle, make little sense. Also, the color scheme is WAY to monotone, and the renders have bevels (bad) and the render edges do not appear to be blurred. IMO: 2.0/10.0
~~~~~Some Tips~~~~~
Renders: Use Ctrl + T to open the Free-Transform mode when the render is selected. Hold shift and drag one of the corners out to scale the render up. Hit enter when you are finished so fix the resolution of the enlarged image.
Brushes: Try to use a variety of brushes when making background artwork. Also, getting effcient with blending render and brushwork together will be a very big help to you in the future. Take my sig for example, 1 Silver Surfer render, adjusted using Free-Transform, and the rest is pure brushwork.
Colors: Try to use a variety of colors when making any peice of art, but make sure the colors coordinate, rather than clash. Bright colors tend to clash, as does say purple and green, red and teal. Google a color wheel and learn about the colors, their analogues ect.
Just be creative, experiment, check out some tuts, and ask questions. IF you don't know how to do something, or wonder if it can be done, ask us, and we will tell you and/or test it out to see. Keep practicing.