The man's head is bowed in silhouette. Above is a guard tower; below are the words "You are not forgotten." And three decades after a former Army pilot first sketched the stark image to commemorate those missing in action from America's longest war, it has become an enduring emblem of Vietnam, a flag second in popularity only to Old Glory itself.

The POW/MIA flag was created in 1971 by the National League of Families of American Prisoners and Missing in Southeast Asia. The POW MIA flag was created in memory of those missing or captured in Vietnam, but to veterans organizations it has come to represent all the missing from U.S. military actions dating back to World War II, a group totaling 88,000. Most are from World War II; fewer than 2,000 are from Vietnam.

It first flew over the White House in 1988 and was installed in the Capitol Rotunda in 1989, making it the only flag ever permanently displayed there, according to flag experts. And in 1990, Congress adopted the POW MIA flag as "the symbol of our nation's concern and commitment to resolving as fully as possible the fates of Americans still prisoner, missing and unaccounted for in Southeast Asia."

Congress later passed a law requiring that on six holidays the POW MIA flag be flown at all post offices, the Capitol, the White House, national cemeteries, military bases and the memorials for the Korean and Vietnam wars. The holidays are Armed Forces Day, Memorial Day, Flag Day, Independence Day, Veterans Day and National POW/MIA Day (the third Friday of September).