Toynbee Tiles

Have you ever heard of Toynbee Tiles? I certainly hadn't. They are small (roughly license plate sized) plaques consisting of linoleum pieces and asphalt glue that consistently carry the same message:

TOYNBEE IDEA
IN MOViE` 2001
RESURRECT DEAD
ON PLANET JUPITER.

The tiles are found in a number of major cities throughout the United States and even as far away as a handful of destinations in South America. It's never been made clear exactly what the message means and the Wikipedia entry hardly clarifies anything (though I do love an entry with that many Citations Needed).

There's a great NPR article from 2006 about their existence, their potential meaning and history and a heads up on Justin Duerr's documentary Resurrect Dead. I am, to say the least, quite intrigued to find out more.