A chit is an IOU, acknowledging that a debt must be paid.  “Blood Chit” is what Armed Forces aviators call a piece of cloth they carry when they’re operating in a combat zone.  It’s about as wide as a man’s handkerchief and a bit longer.  It acknowledges a special kind of debt.

A “Blood Chit” serves as an Armed Forces aviator's last survival tool employed when all other methods of evasion and escape have failed in a combat zone and the aviator considers assistance vital to survival.   The United States military's present day doctrine on Blood Chits is contained in the Joint Publication 3-50 "Personnel Recovery".

The message on the cloth is in two parts.  First, there’s the Stars and Stripes, which takes up a third of the space.

The second part of the message is written in the language of every country or tribe the aviator might contact.  It states that the bearer is American, doesn’t speak the local language, has suffered “misfortune,” and needs protection and assistance.  The brief paragraph ends by asking the reader to return the aviator “to my people,” and promises a reward.