The Prisoner of War Medallion is a medal awarded to UNSC personnel who have been captured (POW) in combat by enemies of the UNSC. It is an honorable decoration, though few humans have it. The Covenant do not take prisoners, except the occasional straggler to execute for sport or when one is needed to activate Forerunner technology. There are few other enemies of the UNSC that the military contends with, so the medallion is a rare sight.
As of 2552, the Prisoner of War Medallion is the only service medal that has not been awarded to John-117. There was one event however, when his team should have received this award following their capture by the United Rebel Front at Camp New Hope. Despite this, the medal was not awarded, perhaps due to political reasons. John-117 may also have been eligible for the award following his detainment by the Gravemind on Installation 05, as well as his capture and interrogation by Covenant Loyalists while aboard the Forerunner Dreadnought prior to its arrival at Earth.