Featured in this lot is this 1930s United Airlines foil advertising sign made by Clayton Knight (1891-1969). American aviator Clayton Knight served in World War I and was also a writer, illustrator, and artist in the field of aviation. During America's pre-World War II neutrality, he also played a key role in the recruitment and training of American fighters who were sent to Canada to train and fight for the Allies. Knight specialized in the illustration of aviation books and amassed a sizable collection of airplane artwork. From 1910 to 1917, Knight, who was born in Rochester, New York, studied at the Art Institute of Chicago. Knight volunteered for the U.S. Army Signal Corps in 1917 while enjoying a successful career as an artist in New York with the goal of becoming an aviator. In the summer of 1917, 150 American pilots were sent to England for advanced training, and he was one of those who succeeded in achieving his goal. Knight served in France with the British Second Army and successfully completed missions for the Royal Flying Corps and Royal Air Force. Knight's aircraft was shot down and crashed over German territory in the autumn of 1918. He was a POW recovering in a German clinic after surviving the crash. In order to continue his career as an aviation artist, Knight went back to New York after making a full recovery in a British hospital. He worked together with his artist/designer wife, Katharine Sturges, to illustrate children's books. He published books about his experiences in World War I that he both wrote and illustrated. Knight was appointed as an official artist for the Central Pacific, Aleutian Islands, and Alaskan Army Air Forces. He had a second job as a historian. A large portion of his original works of art, wartime papers, and personal diaries are kept at the Air Force University Library and Historical Branch. Knight was appointed an Officer of the Order of the British Empire (OB) on July 10, 1946 in recognition of his assistance to England during both World Wars. The advertisement shows a metallic look as it was created using colored foil. The ad depicts a United Airlines DC-3 flying over the San Francisco Bay in the middle of the night while the city lights and moon light up the scene. The airliner shows a silver metallic color and reads, "United" on the left wing in black lettering. On the body of the plane it reads, "United Air Lines" in black lettering and the tail wing reads, "NC 16060 / U.S. Mail AM 1-11-12 Express" in black lettering as well. At the bottom of the scene you can see the Golden Gate Bridge lit up with lights as a ship passes underneath it. The sky is full of glowing stars and a bright full moon. In the bottom right it is signed by the artist reading, "Clayton Knight" in silver foil. In the bottom middle below the art it shows the title reading in small black lettering, "United Air Liner Over San Francisco Bay". The art shows good condition with some creasing throughout but no foil loss is present. The artwork measures 20 5/8" L x 15 5/8" W.