Official crew patch of Expedition 51 during their mission to the International Space.
From as early as the 11th century, coats of arms have been used as emblems representing groups as small as families to as large as countries. The Expedition 51 patch is designed as a modernized international coat of arms, blending the traditional shield shape with our modernized symbol of achievement, the International Space Station. The background represents our home world and its inhabitants on the left, and outer space to the right. The bi-color International Space Station is the bridge between the two, symbolizing the benefits on Earth of space research, and at the same time our mission to explore deeper into space, on a path to further discovery and knowledge.
https://www.flickr.com/photos/nasa2explore/25118126302/
http://www.collectspace.com/ubb/Forum18/HTML/001284.html
https://www.nasa.gov/mission_pages/station/expeditions/expedition51/index.html (PDF)
NASA