I actually really like the way it's turned out. I personally don't have too much issues with the edges.
Only thing would be text~ I think it stands out too much and it's too big. I would use a pretty small font~
As for the hand.. hmm.. well I didn't think it was too bad when I looked at it, cos it looked like she was leaning on the render or something, but if you wanna try something out, I would try um.. hm.. how do I explain..
OK I did a rough one on your sig to show you what I kind of mean:
Add a gradient or some sort of texture that acts like the thing she's leaning on? How I did it was..
1. Create a new layer (and put it underneath your nana stock)
2. Select white as foreground colour.
3. Click gradient tool.
4. Make sure the gradient colour is white > transparent (adjusted in the top right corner). Play around until you get the right amount of gradient.
5. Apply gradient downwards (hold shift so that your gradient is straight)
6. Use select tool to delete the top half.
7. Reduce opacity (if required/you want to).
8. Get a laaarge sized eraser, put it to 0% hardness (for edges) and then use the edge of eraser to rub out sides of the white gradient soflty so it doesn't stick out the whole way... it looked like it was cutting the sig in half when I didn't rub it out.
There's probably more ways to make it look a little better but that'll require some experimenting xD You might wanna play around with it ab bit so it blends better, like maybe blurring it a bit so it's not so sharp (dunno how that'll look) etc~
And you don't have to do it, just an idea that might work.
It would also make a nice excuse for putting text on, haha, so you can put the text lined in with the horizontal line (nana on top, Mika Nakashima below the horizontal line) or something like that~ So the text doesn't look too randomly placed.
But I like what you got xD