Museum of Hoaxes has a fairly extensive thread on shoefiti under the subject, "Secret Powerline Codes." It incluces lots of comments from people around the world with their own theories on why the shoes are there. Interestingly, it includes at least two comments from posters who mention that they’re cops. Here’s what they had to say about this phenomenon:
As a police officer I can tell you that these signs are not urban legends. We look into these signals very closely and monitor each area. If you see such a sign please report it to the local authorities as it is common knowledge among officers of the law in most big cities.
Posted by Alex on Sat Aug 13, 2005 at 10:05 AM
I am also a police officer and don’t visit the red light district of Krispy Kreme. Ha ha. It is a trend that is picking up in the community I work. I came here for information about that very topic (Tennis shoes and utility lines) even if it is not a sign of drug or gang activity we remove them immediately.
Posted by Lisa on Mon Aug 29, 2005 at 05:05 AM
Lisa’s comment reinforces my earlier comment that shoefiti is still litter or vandalism, so it should still be removed even if there isn’t a direct tie to drug or gang activity.