The Expedition 12 patch represents both mankind's permanent presence in space and future dreams of exploration. The International Space Station (ISS), featured prominently in the center, will continue to grow in its capability as a world-class laboratory and test bed for exploration. The vision of exploration is depicted by the moon and Mars. The star symbolizes mankind's destiny in space and is a tribute to the space explorers who have been lost in its pursuit. The Roman numeral XII in the background signifies the 12th expeditionary mission to the ISS.
http://spaceflight.nasa.gov/gallery/images/station/crew-12/html/iss012-s-001.html
NASA