From Vera T Velde, a fascinating list of experimental findings that validate the 'broken windows' hypothesis - some evidence of law/norm violation will encourage people to break others. For example,
Bikes are parked in a row next to a fence with a conspicuous "no graffiti" sign, and flyers are attached to each bicycle such that they must be removed to use the bike. If no graffiti is on the fence, 33% of subjects will litter their flyers. If graffiti is on the fence, 69% will. This was so surprising that a news station paid the researchers to replicate the study while they watched from rented rooms looking down on the area. The finding replicated very closely, and now the Netherlands requires immediate removal of graffiti.
This reinforces the importance of choice architecture - framing of the environment in which human beings engage or transact - in designing public policies that can induce behavioural change. For example, consider the case of littering and cleanliness. Since the best choice architecture of keeping the place clean is tautological, a next best alternative is to keep exceptionally clean certain important locations within each city or neighborhood - say, the public transit station, park, an important pedestrian shopping area etc - and then use them to as cognitive reminders. This coupled with aggressive awareness campaigns can be a powerful strategy in the more effective implementation of campaigns like the Clean India program.