This $5 bill with something stamped on its right end caught my eye in circulation.

The stamped design shows a person's head in silhouette with a guard tower behind, what might be a strand of razor wire running horizontally near the chin, and the letters POW*MIA above. There may be more lettering intended below the central design that I can't make out.

Given the design elements and familiar acronyms for "Prisoner of War" and "Missing in Action," a military theme is clearly intended.

I suppose it was stamped onto the note to encourage people to remember those who have been prisoners of war or who have been categorized as missing in action.

But this is a Series 1999 $5 bill. Isn't it unusual that this overstamp appears on this note?

I'm curious. Can anyone shed light on the source or specific meaning of this overstamp?