Now it can be told:

the Canadian Mint’s issuing of a quarter with red poppy highlights
honouring th[e] country’s war dead in 2004 … created an uproar in the
corridors of U.S. Intelligence. Officials down south had never seen
anything like it and became suspicious when an agent found one in a
rental car. Documents released under the Access to Information Act show
concerned contractors described the coin as being "filled with
something man-made that looked like nano-technology."

"It did
not appear to be electronic (analog) in nature or have a power source,"
wrote one of those who examined the mysterious ‘device’. "Under high
power microscope, it appeared to be complex consisting of several
layers of clear, but different material, with a wire like mesh
suspended on top."

This analysis

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. 

The alert was later rescinded as "a mistake."  Canadian officials have not yet been asked for an apology or for reparations.  Story here, more here.