From my observation, it seems like adding posts or comments counts less than getting them shared. I don't think that it's in the open source code (or at the very least I can't recall that bit), but I had one weekend when after a series of well-received posts I got two or three dots added to my badge-o-meter. Perhaps it also depends on how much clout users who share the post have themselves? ;)
Either way, it's a slow boil. A bunch of people (or a person) making ten accounts and sharing among themselves is easy to spot and stands out like a sore thumb. With gangrene.
I don't know the internals well enough, though. Even if my approach is clever (thanks by the way! :D) it's no doubt harder to implement than
that my mind was able to cook as a condition.
(if (and (map is-full-user 'list-of-users-who-shared-post)) show not-show)