Several pieces of art have been left on the moon during the missions to its surface. These are the two that I'm aware of, though there may be more:
— a tiny piece of ceramic wafer on which six artists (Robert Rauschenberg, David Novros, John Chamberlain, Claes Oldenburg, Forrest Myers, and Andy Warhol) drew pictures. It was attached to a leg of the Intrepid landing module (though this was never confirmed by NASA) which landed on the moon and was left there in November 1969. Warhol contributed the rocket/penis in the upper-left corner.
— An aluminum sculpture of a humanoid figure that's supposed to represent an astronaut in a spacesuit. It was left on the surface of the moon on August 1, 1971, next to a plaque listing astronauts and cosmonauts who died in the advancement of space exploration.
So we've left a picture of a penis on the moon, as well as a sexless humanoid figure. I wonder if this will confuse future alien archaeologists who find the art.