There's probably no need for the groups to signal each other's existence.

When a new Secret Even Less Wrong is formed, members are previously formed Secret Even Less Wrongs who are still participating in Less Wrong are likely to receive secret invites to the new Secret Even Less Wrong.

Nyan_sandwich might set up his secret Google Group or whatever, invite the people he feels are worthy and willing to form the core of his own Secret Even Less Wrong, and receive in reply an invite to an existing Secret Even Less Wrong.

That might have already happened!