A fork action, would be the recording of the act of forking in such a way that that information could be used by other parites - such as to notify people.
The simplest recording would be to add a fork action to the journal of the page that has been forked.
Fork Editing
Maybe, the notice should not be on fork but on first content change following the fork.
Issues
It might be tricky to come up with the reverse address. And it couldn't work when the client's origin is behind a firewall. But this could be tested.