A "blood chit" was a note stitched to the backs of American pilots to
tell the Chinese that they were friend and to give them safe refuge from
the Japanese and the Chinese communist enemies.
The most valuable of the blood chits were the leather chits with the
American flag CBI (China Burma India) Blood Chit WWII. They were
first used by the Flying Tigers, and later by all airmen of the
China-Burma campaign after the USA formally entered WWII.
An elaborate WWII leather blood chit
Above is a 16 piece goatskin leather blood chit, original WWII with a
2010 value of $750.
The Kanji text in the above pictured chit says in English:
"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."