I live in Japan and I do this and I see most people do this. I like it a lot. It can be for Thank You or I'm Sorry. It helps calm my frustrations when someone cuts into my lane suddenly.
Originally Posted by
AlwaysAisle
I was reading Japanese news and I learned that there is unwritten acknowledgement between drivers in Japan called "thank you hazard light." When you were allowed to change lanes or were let into the lane there is thing called "thank you hazard light" where you turn on hazard light for short period of time (few seconds) to thank a driver who let you in. I did not know that. Obviously this is not a proper use of hazard light as far as traffic regulation of Japan is concerned, but seems to be common thing and many drivers in Japan are aware of that.
In the U.S. I wave my hand to thank a driver who let me in or let me merge. Disadvantage of this is cannot see during night.