I'm just going to say right now, there's nothing to be too harsh about. But, I like to give constructive criticism, so I'll start.
The text takes a big spot within the sig, thus distracting me from the focal. The render could be moved towards the center a bit more, as it looks like it's floating out of proportion. The color of the sig can always mess it up. What I do is color via gradient maps and photo filters. I barely use channel mixer, as if it's too strong, the outcome isn't as great as wanted. It looks as if you pasted in a render, used a default texture, and then channel mixed it. I don't recommend any of that. Although, using some defaults is good, none were needed in this piece.
OH. And how you said it took 5-10 minutes. My sigs are like an hour a piece, because I take my time and look for as many errors as possible. I usually work on it for 30 minutes, go get a drink, wake up my eyes, and look at it again for errors. I recommend looking over everything as much as possible.
