Reading Ivan Vladislavic’s lovely book recently ‘Portrait with Keys – Joburg & what what’ (Umluzi Press, 2006) I was struck by his mention of a ‘tomason’ on p.175:

The term ‘tomason’ was coined by Genpei Akasegawa to describe a purposeless object found on a city street. He has tracked and tagged hundreds of them in Japan and other parts of the world. A tomason is something that has become detached from its original purpose. Sometimes this detachment may be so complete that the object is turned into an enigmatic puzzle; alternatively, the original purpose of the object may be quite apparent and its current uselessness touching or amusing.

It reminds me of another term I love for an object or design that retains defunct features, skeuomorph.