From the US government, the bizarre story of the Canadian spy coin:
The government said the mysterious coins were found planted on U.S. contractors with classified security clearances on at least three separate occasions between October 2005 and January 2006 as the contractors traveled through Canada.
The US government’s subsequent retraction. Including the acknowledgement that the coins didn’t work especially well as a surveillance device if the person could easily use them to buy a cup of coffee or, I’d add, give money to a homeless person.