Hello,
I have tried many designs and here's the only one I'm really satisfied with.
I prefer the question mark as ANC symbol rather than the A as the question mark directly suggests anonymity.
By adding a square to the question mark, it draws a locker and a A. So you can find in the logo concepts of anonymity (the question mark), security (the locker), anoncoin (the A), and coin (the circle).
Here's a few variations in black, white and gray:
http://img4.hostingpics.net/pics/735241ancgray2.pngAnd for those who like colors, I've made a little jsfiddle you can play with (just click the image to pop the color picker)
http://jsfiddle.net/SQ4Jk/5/embedded/result/I hope you like it as it will probably be my last try

AGostrfZbpPSv9rCZQ1vfFrZHYNMbZEZyZ
The last one is my favorite.