Public Displays with History as Social Memory

This is more of a jot for myself.  I am not going to provide too much detail.  But let’s imagine we can keep a ‘history’ on public displays.   Either a history of who’s been near it, a history of what’s been put on it, etc..

How does this element of ‘time’ change the functionality of public displays from ephemeral billboard, to electronic memory — the memory of a shared social space.