This vehicle has its white lights on; what do they indicate?

Correct answer: That it is in reverse.

The white lights at the rear are backup lights. They come on automatically when you shift into reverse and warn that the car is about to back up or is already backing up. To turn or pull out moving forward, you use the turn signal, which is yellow. In the image, the blue passenger car has both backup lights on.

Real Decreto 2822/1998, de 23 de diciembre, por el que se aprueba el Reglamento General de Vehículos