Try having more black and white in it. The signature right now is mostly grey and for Black & White art in general, you want mostly Black & White with some shades of grey. Besides that, I do like the effects that you used in this signature. Maybe strengthen the light source in the bottom right corner cause if you look on miranda's face, the left side of her face is lighter then the right. If you strengthen the light source there, it will help pull the signature in very nicely. These are just my own personal opinions.
like rave said ti could use some more black & whites.
in photography i learned that black & white photos should have a nice variety of shades with strong blacks and whites also.
aside from that, nice placement on both the focal & the text.