Left shoes (as well as other kind of clothes) are usual suspects in cities, it's very often that you can encounter them. Gloves are perfect condidates too but it's less intriguing to understand what happen after a person lost his/her gloves than the shoes. What is even more curious is when you have the pair of shoes nicely dropped at certain places, as shown on the pictures here.
Who does this? Why? Apart from smiling, what happen when you see this?
Anyway, unnoticed by lots of people, this sort of street artifact is part of the cultural life of cities, always refreshing to run across. The peculair ways they are positioned (especially when you have a pair) a good trigger to imagine what could have happened in these situations. To some extent, it forces the observer to try inferring the history of that place.
(First picture spotted yesterday in Amsterdam, second picture three years ago in Zürich)