The origin of the “blood chit” as well - still have one in my office.
I had not watched “Flying Tigers” forever, so I had to look up ‘blood chit” on Wikipedia. They said alternative names were escape and identification flags. That sounds like political correctness to me because it said, “I am an American airman. My plane is destroyed. I cannot speak your language. I am an enemy of the Japanese. Please give me food and take me to the nearest Allied military post. You will be rewarded.”
Now it seems that could be real nice, if the right people picked you up. Yet if they were more concerned about Japanese reprisals, then that would be a problem. Either way “blood chit” looks like a much better name to me.