Oh my, David wants all of us to get technical
Za Signature
Well, its obvious that you have been studying composition. The way you positioned the text compliments the mohawk, almost giving the sig sort of like a second border and definitely allowing the picture to show off itself. Everything about the text, from the opacity to the position in which its in, really compliments the rest of the sig and keeps a natural feeling through out the sig. My only crit about it is that its kinda jaggy/choppy/pixely (whatever you want to call it), see if you smooth it out a bit.
Za Avatar
Well, it seems as if the head has been squished to fit in there. I know it has been rezised, but in the avy it looks kind of abnormal. However I like the text you used, and using a different color for the D instead of just giving it a border does add to the originality. Going back to the picture bit, I actually wouldnt really be able to tell what it is if I havent seen your sig, or your drawing, before. The fact that the facial features have been resized to such a small size that they are barely apparent really makes it hard to figure out its a face, and it looks like an abstract shape. Never the less it still looks good, but if you want it to look like the actual drawing you should focus on showing one main part of it (Maybe just the face?) then trying to get all of it in there.
None of this changes the fact that both of these works of art are amazing, so big ups for you, keep drawing, and have a nice day.