Fork symmetry is the idea that when a person forks a page, both parties should be aware of the action. Currently only the person forking a page "knows" what they have done. The advantage of the fork/forked unification is that the neighborhood expands in a very generous way.
Fork Symmetry is similar to Link Symmetry, and my personal inclination is that it should be the starting point from a design perspective. All links should be bi-directional by default.
The client could tell a remote server when it forks a page. However we don't want strangers to write on any site (they will find a way to spam). However, a complementary notice could be ignored, counted or recorded. All are useful options at various states of growth.