Graffiti Art?

I saw an interesting video today about "Reverse Graffiti". I couldn't figure out what that meant when I first saw the phrase.

I looked up definitions of graffiti. (see below) But, found little to match my idea of it. Today, graffiti has a whole different connotation. It's art, in a way. Even though it is illegal, there are those who wish to express themselves by spray painting (usually) either their personal symbol of their name or some other depiction. There are those who might create a whole, or partial mural.

Definitions of graffiti include:
"scratches, letters and other marks scratched on the surface of a coin in ancient times to identify its owner"

"a rude decoration inscribed on rocks or walls"

"The words or pictures scrawled or scratched in public places, particularly on walls - could be political messages, personal notes, advertising, curses amongst others."

"Graffiti can take the form of art, drawings, or words, and is illegal vandalism when done without the property owner's consent. Its origin can be traced back to ancient civilizations such as the Roman Empire and Ancient Greece."

All that being said, just take a look at the following video.