I have been known to call in, for example, a car parked in front of my house at 3 AM, lights off, engine running. . .and had a patrol car pull up behind it about 5 min. later. . . never did find out what was going on. . .
We had a similiar situation a couple of years ago. It happened on a regular basis, so we thought the neighborhood was being cased. Turned out that a drug dealer lived down the street. He's now gone to the clink. After a few misguided buyers knocked on the wrong door a few times, the problem seems to be gone now. A couple of calls to the police really made a difference.