The first recorded piece of nose art was a sea monster painted on the nose of an Italian flying boat in 1913. This was followed by the popular tradition of painting mouths underneath the propeller spinner, initiated by the German pilots in World War I, and exemplified by the cavallino of Francesco Baracca. After these beginnings, though, most nose art was conceived and produced by the aircraft ground crews, not the pilots.
And here's a patent for a shark-shaped nose for aircraft.
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