I would just use #

Reply to this note

Please Login to reply.

Discussion

That's already been used for hashtags. It wouldn't be able to know if you are looking for a hashtag or a geohash

That's only ambiguous for a tiny number of geohash, sucks to live in #lol

And then maybe even be smart and when some searches for a hash of a known city or country name, return anything with the corresponding geohash too.