What does it mean when someone throws shoes over a telephone line?

I know what it used to mean when someone threw two tennis shoes tied together over a telephone line (or some other suspended thing); it used to mean that you’d be able to find a drug dealer (of various varieties) there. Is that still true? Wouldn’t the cops have figured that out yet? I see shoes constantly in NYC’s Chinatown, and some in Brooklyn and SoHo, but haven’t seen them many other places. Any ideas?