Traces of time and people interaction
Several examples of how people's activity and interaction with objects transform their appearance. Stairs in a bookshop (above), a door handle and the floor of the parisian subway are all victims of the passage of time.
Of course, these traces (or patina) can have an intriguing aesthetic function but they can lead to a specific affordances too: traces that orient action or shape people's interactions with the environment. Social navigation indicators of some sort.