Broken Windows is probably the most influential criminological theory of the last few decades co-developed by James Q. Wilson and George L. Kelling. Wilson passed away a few days ago – read his obituary here – a very able academic, he clearly led a fulfilling and stimulating life. 
The original Broken Windows theory was laid out in March 1982 in this landmark article in Atlantic Monthly and it is still a compelling read. If you have less time, here’s the wiki and for balance, here’s some disagreement from an NGO. Broken Windows posits that the “fear of crime” which is all too often derided by some crimefighters is actually rationally grounded in the connection between disorderliness and urban and social decay.
1982 – 30 years ago – of course was a different world. Spray painting graffiti really hadn’t quite taken off and I do sense there are many fewer actually broken windows than back then, especially in the UK. Both the UK and the USA were then coming out of recession, downsizing manufacturing and ex-factories and businesses with broken windows were frequent sites. Since then, there’s been a lot of urban renewal and in the UK, we brought in Anti-Social Behavioural Orders which went some way to addressing low-level non-criminal offences which nonetheless created a fear of crime and came at a cost to the local community.
So I would argue that graffiti is today a much better indicator of urban and social decay as it is so much more prolific than broken windows. As the original Broken Windows article said at the time to the then emerging trend of subway graffiti in New York;
“As Nathan Glazer has written, the proliferation of graffiti, even when not obscene, confronts the subway rider with the inescapable knowledge that the environment he must endure for an hour or more a day is uncontrolled and uncontrollable, and that anyone can invade it to do whatever damage and mischief the mind suggests.”
Matt says:
It’s interesting that graffiti is viewed quite differently in different countries. In the UK graffiti is seen by many people as an indicator of disorder, but the same isn’t true in other countries. In Germany, the railway authorities (for example) seem to just ignore graffiti.
I wonder what the relationship is between public perception of graffiti as anti-social and the official response to graffiti: are the police and others responding to public perception, or has their response encouraged people to think of graffiti as an indicator of disorder?
Of course, if the police and others did inadvertantly contribute to graffiti becoming a signal crime, there isn’t much we can do about it now. Fortunately, the intervening years have proved Wilson and Kelling wrong in at least one respect: the New York Subway turned out not to be “uncontrollable”, and is now (thanks to many years of hard work by the MTA and police) a very safe place to be.