expression, noun
flashing hazard lights to say thank you
Colloquial term for the driving custom of briefly turning on hazard lights to thank another driver, e.g., after being let into a lane.
from English thank you hazard
前の車がサンキューハザードを出してくれた。
The car in front gave a thank-you hazard flash.
合流したらサンキューハザードを忘れずに。
Don't forget to flash your hazards to say thanks after merging.