Who or what is a Toynbee?

And what are these 'tiles'? Several questions recently have challenged Atheists about 'Toynbee Tiles' - I'm utterly baffled! Is this an American thing? Someone explain please!
The question is in the R&S section because it is a specific response to questions posted here implying that atheists have something to do with the tiles (The questions did not define what the tiles were, which is why I'm asking!) As they seem a very real phenomenon, I don't see why it should be in the M&F section!
Thanks for the link, I know understand what they are, but I'm still baffled by the atheist association!