From NPR : French Families Adopt U.S. Graves in Normandy :

Eight years ago, a French couple founded an organization that adopts graves of American servicemen who died during the Normandy invasion of World War II. The volunteer group encourages French families to lay flowers on the graves when the Americans' own families can't do it.

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If there is a more honorable overseas observance of the U.S. Memorial Day, I'm not aware of it.