Basically Users campaign it to tell single occupant vehicles that they are the reason for added pollution and thus you can no longer see the volcanos due to smog. Pretty crazy campaign for sure."Drivers stuck in traffic in Mexico City lately have found themselves being buzzed by a fleet of sign-toting drones. “Driving by yourself?” some scolded in Spanish. “This is why you can never see the volcanoes”—a reference to the smog that often hovers over the mega-city and obscures two nearby peaks."
See more of this story over at Technology Review --> Uber’s ad-toting drones are heckling drivers stuck in traffic