Maybe you just notice them more in some areas. Around here in Austin, there are sneakers hanging off telephone wires in every neighborhood in the city, especially near the high schools. All of them, even the whitest ones, even the rich neighborhoods. It seems to be a high school thing. So I don’t think it’s a black/ghetto thing; I think you are just more likely to be observing your surroundings in those neighborhoods, whereas you take for granted your own neighborhood and don’t observe it so closely.