Thanks @jolyon That really helps clarify it.

@mix said something interesting in this context about running a server with a different key which I'm guessing uses the same mechanism that you are describing.

It's possible to make your own private network using your own pubs (or running peers just locally) and running with a key which means they won't share info with anyone else not using that key. This is like running a parallel universe.

If one of the domain experts could clarify how "sign" works and that nature of leaking/joining two networks that would be really helpful :)