In emergency, the term "green passage" is often used, which is a passage specially opened to express faster and simpler, to save life and time, and to omit complicated processes. But I'm not sure what you mean by green sign. Because as far as I know, a common sign of emergency first aid, especially pre-hospital first aid, is the blue hexagonal star called the "Star of Life". This is a blue six-pointed star with a white snake stick in the middle. The six corners above represent the six elements of pre-hospital first aid, and the snake stick is a universal medical symbol in the world.