The worried contractors described the coins as "anomalous" and "filled with something man-made that looked like nano-technology,"

The confidential accounts led to a sensational warning from the Defense Security Service, an agency of the Defense Department, that mysterious coins with radio frequency transmitters 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.

Poppy quarter led to spy coin warnings.
The surprise explanation behind the U.S. government's sensational but false warnings about mysterious Canadian spy coins is the harmless poppy quarter, the world's first colourized coin.