First one is best imo could use a bit more contrast but i like. Also I think his chest could be darkened and the light should be coming from over is right shoulder(left if people wana get technical :| ) 2nd one looks nice but no offence cause im sure im wrong but it looks more like a render put on a background with little actually done to it, but looks nice, just could use some more effects I think. 3rd one is blegh not so hot theres no real flow to the signature and looks like ya just splashed around the liquify tool. Background needs work, should define your focal with some kind of letting effects or by making the background focus on it some way. Your 4th sig I think looks really nice but black and white doesn't really fit superman, just an opinion again take what ya will. I like the background, except the 2 random splotches of black in the bottom left corner of the sig. also mabey work on right side of teh background, because the left is nice and some interesting brushing, while as move over to the right it gets plain and un interesting.
They all look nice, like iron man and super man the most. You definetly should make some tutorials of your sigs, you can eran much when posting in paid tutorials. Sure they will be bought, they are worth it. Keep up the work.
