Photo: 2cauldrons [Flickr]
Leonardo da Vinci's Mona Lisa is so iconic that her smiling face has even shown up on graffiti. WebUrbanist has a neat post about 8 such unauthorized appearances by La Gioconda in the streets all over the world.
This one above is the RPG Mona Lisa, by the British street artist Banksy in Soho London.
http://weburbanist.com/2008/07/05/8-postmodern-appearances-of-the-mona-lisa-classic-subject-resurfaces-in-urban-street-artworks/ - Thanks Jon Jason!