These two ash-tray found in Geneva and Lausanne are two impressive examples of an object affordances:
Why do I blog this? This is utterly curious from a design perspective. the artifacts designed to received trashed objects looks like the object itself. A sort of recursive affordance to some extent. What does that mean? It's actually not that recursive and the second example if maybe more self-explanatory since the two different garbages are next to each other. Besides, the first one has a little hole that only allow to receive small things like cigarettes.