ANN ARBOR, MI – Lakhvir Sohal, a rising senior at the University of Michigan, knows what he’s going to do to celebrate graduation – throw a pair of shoes onto some power lines near his rented house.

NEWARK, N.J. — George Williams has no doubt that the gray suede tennis shoes dangling from the telephone wire high above his house on 18th Avenue in Newark signify that drugs are sold there. Not long ...