“National POW/MIA Recognition Day was established in 1979 through a proclamation signed by President Jimmy Carter. Since then, each subsequent president has issued an annual proclamation commemorating the third Friday in September as National POW/MIA Recognition Day. National POW/MIA Recognition Day ceremonies share the common purpose of honoring those who were held captive and returned, as well as those who remain missing.”
https://www.dpaa.mil/Families/Posters.aspx
Learn more:
https://www.pow-miafamilies.org/recognition-day.html