Symphony No. 2 by Rachmaninov, Pastoral Symphony by Beethoven, and Piano Concerto No. 2 by Shostakovich have all been used around the world to deter loitering with great success. Although studies on the effect of this technique are scarce, the belief is classical music acts as a social deterrent for would be vandals.
A quick search around the internet will yield multiple articles supporting this belief. One supporting article from the Columbus Dispatch talks about the success a YMCA located downtown in Columbus, Ohio had using classical music as a deterrent. In early 2013, Sue Darby had a couple of guys outside the Downtown YMCA in an escalating argument. Rather than intervening, she simply increased the volume of the classical music playing on the speakers located on that side of the building. This prompted the two men to walk away. “I feel like it’s a positive approach,” said Darby, executive director of the Y, in Downtown Columbus. “People don’t tend to stand around. There’s a sense of security.”
My Graffiti Removal Guy suggests property owners use classical music as a graffiti deterrent in conjunction with other prevention methods. Keeping the property clean and properly maintained will also help. If you don't have vandal proof speakers, make sure your speakers are in a safe place. In West Palm Beach the police said the classical music program failed because the loiterers destroyed the speakers.