This is a very good drawing. It feels like you've put in a lot of effort to get the form/lines looking good. Possibly bring the jaw line in very, very slightly as Zhang Ziyi has a pretty, pointy chin. (see below)
The shading looks a little stringy. That may be entirely what you are looking for to demonstrate the flow of texture, but I would go over it lightly until it has less contrast in each mass section.
Are you going to paint this? I would like to see it if you do.
A huge and scrawling signature can overpower and damage the presentation of a picture, appearing egotistical and amateurish, which doesn't match such a beautiful drawing. An artist's signature is a way to determine who created the piece, and this is important for getting your name out there. It is also a stamp of sorts. Often artists will make their signature kind of like a miniature drawing in itself - very simple, clear but also relatively small. Ultimately, your goal is to create an identifying mark that can be recognised by the viewer.
Post more of your drawings! ^_^
