A broken window is a physical symbol that the residents of a particular neighbourhood do not especially care about their environment and that low-level deviance is tolerated. The theory influenced policy-makers on both sides of the Atlantic and, most famously, in New York in the 1990s.  

Their response was zero tolerance policing where the criminal justice system took low-level crime and anti-social behaviour much more seriously than they had in the past.  This included "three strikes and you're out" policies where people could get serious custodial sentences for repeated minor offences, such as unsolicited windscreen cleaning, prostitution, drunk and disorderly behaviour, etc. 

The idea was that low-level crime should not be tolerated and severe penalties needed to be meted out for anti-social behaviour and minor incivilities in order to deter more serious crime and ensure that collective conscience and social solidarity is maintained by clear boundary maintenance.

Evaluating Broken Windows Theory

• The impact of the policy in New York appeared to be dramatic with crime levels (including very serious crimes like murder) falling rapidly. There was a 40% drop in overall crime and over 50% in homicide. Fans of Broken Windows on the political right in America hailed this as a success, but there are two main criticisms.
• This policy coincided with a period of economic growth and a reduction in poverty.  Those who feel that social conditions are a stronger driver of crime than broken windows suggest that the crime rates in New York fell because the social conditions for people in New York significantly improved. As such it is possible that it was purely a coincidence that it happened at the same time as the implementation of broken windows. Just because there was a correlation does not mean that there was causality.
• Some accused Broken Windows of achieving control without justice. Yes, the crime rates fell, but people were in prison, sometimes serving long sentences, for very minor misdemeanours.  Furthermore, there was evidence showing that the policy impacted much more heavily on minority ethnic groups, particularly African Americans and Latin Americans, than on the majority white population.  While poor black people might be arrested for public drunkenness or jay-walking, white middle-class students celebrating the start of their freshman year by doing the same things are tolerated. Therefore, police discretion makes the implementation of broken windows unjust. Supporters of the theory, however, would counter that zero tolerance should mean zero tolerance and white students shouldn't get away with public drunkenness either.