Social norms are powerful things. Some people did a study at the Petrified Forrest National Park on how to prevent people from stealing pieces of fossilized wood. When they put "Many past visitors have removed the petrified wood from the park, changing the state of the Petrified Forest’" on signs the amount of theft was much larger than anything else they tried[1]. So if you're running a public awareness campaign emphasizing how many people break the rules is just about the worst thing you can do. The message DARE seemed to be giving me when I was a kid was that drug use was normal.

[1]http://www.niu.edu/user/tj0bjs1/papers/cdsbrw06.pdf