AD sez, "Girls Guild is an ancient secret society complete with a mythological back-story set in Atlantis, secret code and handshake, nemesis, and (perhaps) soon-to-be-ubiquitous symbol -- but with a twist: all of the secrets, iconography and legends are available for retooling, embellishment and propagation under a Creative Commons license."
This looks like fun, notwithstanding that Girls Guild appears to be so ancient as to have predated the apostrophe.
Introducing Girls Guild
(Thanks, A. D. Ammann!)