None of your sigs seem to have a lot going on in them. Due to the lack of effects, the potential depth of the sigs is ruined. Try placing things in the foreground, as you're aiming to make this sig look as 3D as possible, not flat.
I would also suggest working on your colours. Try not to only use different shades of the same colour, this is what we call "monochromatic" sigs.
Zen is right, but still great effort for a beginner, I'm sure with time and learning you will be able to do some really good works, just keep up the practice and tutorials