This is one of the world’s most infamous stamps.
William Robey in 1918 went to the Post Office and bought 100 of the these stamps when they were first issued. All of them had the bi-plane inverted. They were the only stamps to have the JN-4H bi-plane inverted. It was an instant hit as Robey sold the stamps for $11,500. Last year a perfect “Inverted Jenny” (named after the bi-plane on the stamp) was sold for $825,000.