"The most tangible evidence of this comes from North Korea, which has long made, sold, and itself used GPS jammers.  In 2012 North Korea attacked South Korea with a massive GPS jamming campaign.  The jamming began in late April and continued for over two weeks.  It took less than a day to confirm that the signal was coming from North Korea and was mainly aimed at the South Korean capital (Seoul).  The jamming had little impact inside the city itself (the ground based jamming signal was blocked by buildings and hills) and was only noted by several hundred aircraft landing or taking off from local airports and over a hundred ships operating off the coast.  In all these cases the ships and aircraft had backup navigation systems, which were switched on when GPS became unreliable.  This is how navigation systems, especially those that rely on an external (satellite) signal are designed." 

"This was the third time North Korea has used GPS jamming against South Korea.  For most of March, 2011, North Korea directed a GPS jamming signal across the border towards Seoul.  A separate jammer has been directed at cell phone traffic.  The GPS jamming signal could be detected up to a hundred kilometers south of the DMZ." 

North Korea in grave violation of covenants regarding navigational signals, international and local.  Such BEHAVIOR WARRANTS THE EXCLUSION OF NORTH KOREA AIRPLANES WHETHER CIVILIAN OR MILITARY FROM ACCESS TO THE INTERNATIONAL AIRSPACE.  ALSO THIS TRUE FOR MARITIME TRAFFIC TOO!! 

From "Draft Outlines of an International Code, Volume 1" By David Dudley Field

"False colors and signals." 

"61.  The displaying of false colors, or the making of false signals by a ship, with intent to mislead any ship, public or private, of another nation, is a public offense." 

GPS JAMMING NOT NECESSARILY FALSE COLORS AND SIGNALS BUT VERY CLOSE! 

EVEN FROM THE TIME OF YORE WHEN PIRATES WERE BOLD, THE USE OF FALSE NAVIGATIONAL SIGNALS A HANGING OFFENSE.