The long standing common sense that a place that looks trashy will lead to more trash has unsurprisingly been proved correct.
A few broken windows in an empty building quickly lead to more smashed panes, more vandalism and eventually to break-ins. The tendency for people to behave in a particular way can be strengthened or weakened depending on what they observe others to be doing. This does not necessarily mean that people will copy bad behaviour exactly, reaching for a spray can when they see graffiti. Rather, says Dr Keizer, it can foster the “violation” of other norms of behaviour.
I’m fairly certain the application from this is quite obvious.