From "Homemade AI drone software finds people when search and rescue teams can't" https://news.ycombinator.com/item?id=41764486#41775397 :

> {Code-and-Response, Call-for-Code}/DroneAid: https://github.com/Code-and-Response/DroneAid

> "DroneAid: A Symbol Language and ML model for indicating needs to drones, planes" (2010) https://github.com/Code-and-Response/DroneAid

> All but one of the DroneAid Symbol Language Symbols are drawn within upward pointing triangles.

> Is there a simpler set of QR codes for the ground that could be made with sticks or rocks or things the wind won't bend?