There are many different reasons for hanging shoes from tall structures. Each community has their own reasons.
In urban areas, a pair of shoes is hung from the telephone wires in remembrance of a victim of violence in the neighborhood, often a result of drugs or gangs. I do not have a web reference for this, my friend who used to live in inner-city New York gave me this inside info about why the shoes were hanging on his street.
Many colleges have the tradition of hanging shoes from a tree on campus. Some are a part of a hazing or initiation to a sports team or fraternity/sorority. At a school in Maryland, the 'shoe tree' is open to all students, and contributions are made in twos by the couple... a couple throws both their pairs up on the branches when they first do it - whether it's the first time doing it period or the first time doing it on campus.
This tradition has been observed and transformed for many different geographical areas, with different symbolism for each sub-culture. I would say any answer you get is probably a right answer, at least for the area where the person grew up.