It would be great if you could emphasize more in the Number's carving, a higher contrast perhaps? You should also move them down so their top bit don't get hidden by the border. Tiny but notable mistakes like this can always be avoided - with a little effort when finalizing your works, please do keep that in mind.
I agree with San on the issue of the carvings of the numbers. At first glance I read the "I" as a scratch on the book, but that was before I even realized there's a whole set of these.
I think the icon overall would benefit from some increase in contrast and saturation aswell. The belt kinda looks flat to me on the small scale image, since there's not much shading on it nor a highlight that would indicate it wrapping and dropping at the right edge of the book (while there is a highlight on the left edge).
Other than those nitpicks I quite like the overall design of the icon, I like the twists and curves of the belt.