The way I hear it, running shoes hanging from power or telephone lines, are usually found at intersections, or at least on significantly busy streets. They are apparently advertisement for drug dealers. They say "We sell drugs here." and I have no reason to doubt it!
Not aware of any gangs in my neighbourhood (but what do I know), but I DO know that drugs are sold in my neighbourhood.
Hate passing by the runners hanging 2 blocks away, but they're WAAAY up there - can't be easily to remove em!