It might also be used in marketing, or for a social message. You can understand why they call this reverse graffiti because it is exactly the opposite. And you are not hurting anyone's property, but you can understand why people might be upset about this, or why it draws negative attention to the practice. Some cities now are coming up with ordinances against the use of reverse graffiti, generally because perhaps city council members are upset that other candidates are using it against them.