This is incredibly clever – while showing a normal advertisement at a movie theater BMW shot a flash from behind the screen. The end result of the flash was that when the ad ended and viewers were asked to close their eyes they would see the BMW logo with their eyes closed. This works in the same way as staring at a bright light (the Sun) will cause you to see bright spots when you close your eyes. Very clever.
I think if this happened to me I would be the guy sitting there begging for them to do it again…