a memory

When I was about 12, I guess, I noticed that every time I saw a "No Dumping" sign there was trash strewn all around it. I wondered, do people with trash to dump wander around looking for a "No Dumping" sign? When they find one do they think, "Aha, this is the spot?" I pondered this on occasion for two or three years before one day it finally hit me: nobody would bother to put up a "No Dumping" sign except in a place where people had been dumping trash.