Dirt = Crime?

This story fascinated me.

We all have things that red-flag as "criminal" or "suspicious" to our brain - things that for the most part lie in stereotypes of behaviors we've seen before. It is nothing new to say that if I see a movie about gang colors I'll be on the lookout for them when I go into the city. But does seeing evidence of criminal activity (graffiti, drug use) make us more likely to bend the rules? If so, does seeing evidence of criminal deterrence (neighborhood watch signs, impeccably clean areas) produce the opposite effect? Why?

The article mentions that the study's results show a pretty clear spike in minor criminal behaviors (cutting through a gap in fences, tossing litter) when people are presented with an area in which minor crimes (graffiti, locking bikes to a fence next to a "do not lock bikes here" sign) had already been committed. But what of an area in which no crimes were visible - it was just dirty?

I personally don't see dirt as automatically pointing to criminals or criminal behavior, although there does seem to be a strong correlation these days between how clean one's house is, and how high one's income level is, making a strong case for the poorest of us (who are also the ones more likely to commit minor crimes, if you believe statistics) also being the dirtiest - either through lack of caring or lack of cleaning products. But I don't try to add to the mess when I walk through a particularly untidy part of the neighborhood... nor do I get the urge to steal bicycles there. But how many people would? Is it possible that crimes are more common in dirty, run-down areas of cities only because that's where the criminals feel most comfortable committing them, despite the fact that police concentration is likely higher in those parts? If we removed all the police presence from the most wealthy parts of town for a few days, would crime rates rise there? What if we scattered graffiti on the walls of the McMansions?

It's an interesting study, and I'd love to see more that replicate these results in different areas and conditions. If the human mind associates dirt with criminal behavior, I want to know where that idea came from - although I'll probably still let my kids play in the mud.