A blood chit is a written notice identifying a downed flyer as a friend of the locals. It is written in their language and asks for assistance from the locals-- especially in hiding from the enemy and providing the flyer with medical care.
The concept of the blood chit came about in 1793 when French balloonist Jean-Pierre Blanchard was conducting the first balloon flight in North America. Blanchard did not speak English and had no idea where the balloon would touch down so George Washington gave him a letter stating that who ever found Blanchard was to help him return to Philadelphia.
The most famous Blood Chit was carried by the American Volunteer Group in WWII. I'm sure a lot of you are familiar with the Flying Tigers' Blood Chit.
"This foreign person has come to China to help in the war effort. Soldiers and civilians, one and all, should rescue, protect, and provide him with medical care."
It is unknown how the Flying Tigers first learned of the Blood Chit. It is suspected that the RAF in Burma gave the AVG the idea. RAF fliers had carried the earliest chits in The First World War over India and Mesopotamia.
When the US officially entered the war, it issued blood chits to all its fliers in a variety of different language. The practice of issuing chits continued through Korea and Vietnam and continues today.
More information on blood chits:
http://cbi-theater-4.home.comcast.ne...bloodchit.html
http://www.aiipowmia.com/histories/histchit.html
http://www.usmcpress.com/heritage/blood_chit.htm
http://en.wikipedia.org/wiki/Blood_chit