It’s Labor Day 2010 in the United States, a federal holiday, and one of those days Americans are urged to fly the U.S. flag.
The poster was issued by the Office of War Information in 1942, in full color. A black-and-white version at the Library of Congress provides a few details:
Labor Day poster. Labor Day poster distributed to war plants and labor organizations. The original is twenty-eight and one-half inches by forty inches and is printed in full color. It was designed by the Office of War Information (OWI) from a photograph especially arranged by Anton Bruehl, well-known photographer. Copies may be obtained by writing the Distribution Section, Office of War Information