Hello hopefully I read correctly and your shop is open. My requested sig is of an original character created by me so it may give you something a little bit more interesting to do other than stock characters.
1)A bit Longer than the size of the sig I have
2)Yellow shades, black, and white
3)James T. Smiley
4)Some black spots in the background, like ink splats
5)http://m-god.deviantart.com/art/JTS-120372978
6)Maybe rough brush strokes strewn about, somewhat like the SFIV(if you can do it and if not, no problem).
Also just try to focus on the face and torso of the drawing, not the entire figure.
Hopefully you have fun with this and if there are any problems with the information provided please let me know.