Bullies take them off defenceless kids, then sling them up out of reach as the ultimate taunt. Gang members create an informal memorial at the spot where a friend lost his life. Crack dealers festoon wires to advertise their presence in the neighborhood. The shoes increase wire visibility for low-flying aircraft. Overly puffed-up boys who have just lost their virginity or otherwise passed a sexual milestone look to signal the event to others.
Kids do it just because it's fun.
In the Southwest exists a similar practice, that of placing old, worn boots upside down on fence posts by the side of a road. Driving along, one passes upturned boot after upturned boot. When the toe is pointing towards the house, he's telling the world he's home. Members of the military have pointed to the practice of pitching an old pair of army boots over the wires when leaving a post as a possible origin for sneaker slinging. According to some, army boot pitching is a ritual performed upon completing basic training, according to others, the boots are tossed when a soldier leaves one post for another, and a final school of thought holds that boot pitching is properly done only when the service itself is being left.