sorry but to me they just look like renders on top of a background. you need to blend your renders in with your backgrounds to add depth
If these are your first attempts at sig making then you're goin make a killing in this art form. Like Kay said, work on blending them into the background. Duplicate your render layer and smudge it outward, set it to Lighten or Screen and erase parts that cover your focal point or that don't look good.
The first and second sigs are pretty good, the other 3 do look like you just cut the character out and slapped it on a background. Nice job on the fist 2 if this is your first time.
