1. Your render is way to blurry, it should stand out
2. The text is just a font with two streaks of white in it. Be more creative.
3. The render doesn't blend in to the background. Blurring the render doesn't make it blend
4. The render has no effects on it whatsoever, no gradient maps, blending options, lighting effects, anything. It's boring
5. The background is too chaotic, and there is no central theme. It looks like you didn't even create it, and just put the render on top of it.
You can't also classify it as a sig because it's not a signature, it's just large art.
I would recommend Photoshop. It might be overwhelming at first, but it is so much more powerful than gimp.