I saw an article on Yahoo news yesterday, “U.S. warns about Canadian spy coins,” that pointed out a warning issued by the U.S. Defense Security Service about Canadian coins being used to track U.S. government contractors.
The CIA has information about similar types of coins: “This hollow container, fashioned to look like an Eisenhower silver dollar, is still used today to hide and send messages or film without being detected. Because it resembles ordinary pocket change, it is virtually undetectable as a concealment device.”

(more…)