Signs like this one were first spotted in New York and Philadephia in 1996. They appear to be plastic and baked into the street or sidewalk.

The plaques make reference to Stanley Kubrick’s "2001" (and perhaps "2010"), but what do they mean?

Some publicity was generated about the bizarre plaques, and it turns out that these signs appear throughout the mid-Atlantic (e.g., Baltimore, Washington, etc.) and (how bizarre) Argentina, Brazil, and Chile.

Read more about the the Toynbee Mystery and see if these signs are in your neighborhood.