Windows are often the best real-estate on a vehicle. This is because they are usually always at eye level and fairly flat.
Perforated film has little holes in it which allow people to see graphics from the outside while allowing people to see out from the inside. Depending on the angle of the window, the driver may have reduced visibility. This can be solved by using a film with a different perforation pattern. The image on the right shows an example of a rear window wrapped in perforated vinyl.
