I don't like your works.
You got serious problems with text and focial points, only few sigs have this problem half solved. Also most of them are full of bad looking details, do not just use plain brushes, it's just, idk - looks so wrong, you should find more complex ways of doing background presence. There are too much of unneeded/missplaced details.
Also there are problems with composition, placing render in the middle isn't a good choise, unless render requires such a place itself, but in your signatures, middle composition really doesn't look good.
So yeah, that's a short critic about your sig's, you should check out some tutorials, and i wish you luck in becoming better gfxer.
-peace