There's a part in the movie Big Fish where the protagonist, Edward Bloom, loses his shoes to a girl named Jenny Hill. Jenny doesn't want Edward to leave the subtly mythical town of Spectre and indoctrinates him as per the town custom: tying the laces of one's pair of shoes and throwing them over a telephone wire, to dangle out of reach. The logic, ethereal as it is, goes that without one's shoes, one can no longer travel and might as well settle down.
In creating this scene (I don't think the custom appears in the novel) Tim Burton, knowingly or otherwise, contributed his own theory to the reasons why there are shoes inexplicably dangling from the phone and power wires that criss-cross overhead and connect the world. Raise your line of vision just slightly in pretty much any city and you'll notice that there are shoes hanging from phone wires overhead. It doesn't seem all that weird until you start to notice that they're everywhere and if you think about it long enough you'll probably begin to wonder if other people know something you don't.
Such is the allure of the phenomenon known as shoefiti. There are plenty of theories about why people dangle shoes from wires, but none of them have ever been fully vindicated. Most prominent is the explanation that dangling shoes signify a place to buy drugs is very close by. It also traditionally means that the area beneath the shoes is controlled by some form of organized crime, whether it's the mafia in Argentina or a gang in Los Angeles. In Havana they apparently are hung as a sign of protest.
Other theories include that they are the remnant of a momentary joyous ritual of a boy who's had intercourse for the first time (clinical enough?) or that they're thrown after high school graduation, after a marriage or to commemorate the death of a loved one.
There are theories that it's meant as art or to signal a neighborhood that's not uptight, which makes sense when you consider the dearth of shoes dangling in the suburban subdivisions. And, as a poster on a real estate forum points out, they at least in actuality do signal a neighborhood that doesn't concern itself with appearances too much.
A guy who recently made a documentary about shoefiti called Flying Kicks (thanks, Xeno) and a neat blog called Shoefiti is dedicated to tracking and attempting to explain the subject. Since neither of these two sources are capable of pointing to a correct theory, then most likely all or at least most are correct. There are probably shoes hanging from telephone wires that were thrown by a very happy boy or a recent graduate or a mourner. There are definitely shoes hanging from wires where you can buy drugs or where you'll find organized crime, and probably the same pair of shoes are meant to indicate both.
And it's possible that these theories have given rise to practice; that the inexplicable nature of dangling shoes, coupled with the urban legends that attempt to explain them, have given rise to actual practice. Which, if correct, is pretty cool.