I saw a number of the mysterious Toynbee tiles in the streets of Philadelphia last week. The tiles began appearing in the early 1980s and have since been spotted in cities around the world. Most have become worn or have disappeared as streets get repaved. NPR ran a story about the tiles a couple of months ago. One of these days I'll have to go back and take pictures of the known tiles in better light. This guy seems to be obsessed with the tiles.