I own a business across the street from an unused building. For years it had been a site for heroin dealing, vandalism, aggresive panhandling, multiple assults and batteries, and at least one mugging in broad daylight. This, of course, was not good for business.
So I got a high quality netcam, put the camera feed live on a web site, and informed anybody who cared to listen ( this included neighbors, cops, drug sellers and buyers, etc ). It took several months for the problem to go away.
First to disappear were the most obviously affluent buyers. Then, over several months, there was a gradual decrease in traffic, and the last to leave were the most desperate looking ones of the entire crowd – the stone junkies with half their teeth rotted away.
That was about two years ago. Every month or so, someone shows up, still thinking that it is active. They sit there for an hour or so, then give up and go away.