A report in this week's Economist explains that researchers in the Netherlands deliberately created controled settings as a series of field experiments designed to discover if signs of vandalism, litter and low-level lawbreaking could change the way people behave.
They found that they could, by a lot: doubling the number who are prepared to litter, trespass, or steal.
According to the Economist, the message for policymakers and police officers is that clearing up graffiti or littering promptly could help fight the spread of crime. Read more here. A full report on the experiment's findings is published in the current issue of the journal Science (subscription req'd).