This is a particularly clever advert. It is all explained in the video, but in short, what it involves is an advert for BMW being played on a projection screen and during the advert there is a series of flashes behind the screen that project the letters BMW onto the retinas of everyone who is watching.
This is certainly one of the most innovative and ingenious ideas for a conceptual form of advertisement that I have ever come across! The video is definitely worth a watch.
Be seeing you!