He was known for his readymades such as "L.H.O.O.Q.", a copy of the "Mona Lisa" with a penciled-in mustache & beard
The discrete, delicately penciled-in mustache and goatee inscribe into the image
... [DOC] [TLE] DADA Companion -- Marcel Duchamp | Ready-Mades Catalogue [PAR] In 1951 he made a third version for the exhibition 'Climax in 20th Century Art, ... 
Another rack was bought by Duchamp for his sister Suzanne in Paris, 1921.