Sometime in the mid-1980s, somebody — or some group of people — started installing placards in streets and highways, in cities all over the Eastern half of the US. These placards varied in size from something shaped like a US car’s license plate up to something like a poster board. Cut in mosaic fashion out of a flexible, colored, linoleum-like, tile material, these "Toynbee Tiles" were found to be EMBEDDED into the asphalt!

And over the several decade history of appearance of all of these hundreds of tiles — both in the US and in South America — nobody has ever spotted who's doing it. Or figured out why. Or, for that matter, HOW!