US 1962 4c Project Mercury Stamp

Few stamps have a better backstory. The Post Office printed this 4-cent design in secret and shipped it in sealed packets to postmasters in 305 locations, to be opened only if John Glenn's flight succeeded. At 3:30 p.m. on February 20, 1962, after Friendship 7 came home, the word went out and the stamp went on sale that same day. The dark blue and yellow design shows the capsule above the curve of the Earth, captioned U.S. Man in Space. With almost 290 million printed, it is one of the easiest landmarks to add.