Back in the late 70's, a detectorist I knew told me about a trip he took to Boston with a buddy of his, to do some older city sites. They drove all over, in, and around the area, looking for just the right spot. It was just starting to get light out, when they came upon a park. It was a classic, old city park, with wrought iron fencing around it, an old fountain, and big, old trees. They parked, and went right to work detecting. He told me that they started finding coins right off the bat, and that they were all old coins. They were both totally shocked! They were finding bust, seated, barber, and big coppers at will, on almost every signal. They couldn't fathom how this was possible. They hadn't even gone far from where they started, as the signals were rather close together. They had been at it for just over an hour, when a police car pulled up. The officer got out and asked them what in the world were they doing there. They told him what they were doing, and said they didn't realize what they were doing was wrong. He aknowledged that it wasn't what they were doing, but where they were doing it. They asked the officer what he meant, and he told them to look around. He told them they were in a rather impoverished suburb of Boston, known as Dorchester, and that he would stay there only long enough for them to safely exit the neighborhood. After looking around to see half the folks in that area standing around, and in the windows, watching them, they decided they had better heed the officers warning and leave the area.
He told me it was a lesson to him to make sure you are aware of your surroundings.