Originally reported at
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=642350:
Darcs creates a cache directory in the user's home directory. Various
backup utilities can automatically exclude cache directories if tagged
via the "Cache Directory Tagging" standard
(http://www.brynosaurus.com/cachedir/). Doing so requires creating a
file CACHEDIR.TAG in the cache directory, containing the contents
"Signature: 8a477f597d28d172789f06886806bc55". Please consider
implementing this standard by creating this file, so that backup
software can automatically exclude this cache.