After my "pacman" icon
(http://img194.imageshack.us/img194/2015/notmuchpacman.png) was not
appreciated due to a possible "eating mail" analogy :-), I quickly hacked
together another (public domain) licensed icon based on some clipart
from openclipart.org. This one clearly shows that you have not much mail:

http://github.com/spaetz/notmuch-all-feature/raw/master/contrib/notmuch.png

(svg is also there)

I am not saying I like it a lot, but I needed *some* icon besides the
standard emacs icon in my toolbar to launch notmuch.

I hope someone finds it useful.

spaetz