Ford has been putting this on cars and trucks since the mid 80s. This was done in response to the Ford Fireball, I mean Pinto. There were many cases when the Pinto was hit in the rear, the bumper and/or a screw would puncture the gas tank and cause it to erupt into flames. This is also a safety device that shuts off the fuel when the vehicle is hit in the rear.
When I was rear ended last year that freaking thing went off... had a hurt wife, the idiot who hit me (still on his phone after hitting my 6 month old car) yelling at me and cars honking... I forgot about it lol. $8000 in damage later... the kid lost his license, my wife and I got money out of progressive and my car eats through tires still But the moral of the story is... when you are in an accident you forget about that stupid little button easily lol.
My friends tempo got rear ended once from a kid who's parents had just bought a VW, the car needed moved and I was the only one who thought about the fuel cut off and wear to look. I was slick as hell for 5 minutes.