Crypto's larger icons show
Cr but the favicon is
CR. I suspect this is unintended (especially as the current favicon is identical with Code Review's).
I have updated the favicon(both for Main site and Meta). I used Ilmari Karonen's version, and made the "r" one pixel taller per Paŭlo Ebermann's suggestion.
The changes will go live after the next production build(within 24 hours). You may still have to do a hard refresh to see the changes after that.
Generally, as CodesInChaos notes, readability is an issue for lowercase letters at such small sizes. That said, I just tried it, and it is possible to make a fairly readable "Cr" icon at that size:
(The image above is in .png format because imgur won't let me upload an .ico file.)
Anyway, let me hereby relinquish any copyright claims I might have to this image. I suppose the original copyright belongs to Stack Exchange, so if they want to use it in any way (like, say, as the new favicon for this site... hint, hint) they're welcome to do so.