There is an old bug in bugzilla which requests single letter prefix 'c' as a redirect to Wikimedia Commons (bug 4676 [1]), but c: is already configured as a namespace alias for Category namespace (श्रेणी) in Hindi Wikipedia (bug 29940 [2]). I don't know the popularity of use of c: in Hindi Wikipedia, but hope it is ignorable (bug is actually one of the Mayur Bugs :-)).

I hope Hindi community will support bug 4676, which help almost every Wikimedia wikis in every supported languages.

[1] https://bugzilla.wikimedia.org/show_bug.cgi?id=4676
[2] https://bugzilla.wikimedia.org/show_bug.cgi?id=29940