Why is the word police painted back to front on police vehicles?

The reason the Word is inverted is because if a police car is coming up from behind a car, it can be as a stop or just speeding by, but since the Word is inverted on the car when the driver of the car in front of the police car looks in their rearview mirror of their side mirror they can see the Word inverted the right way. Since everything seen through a mirror is inverted, it makes it easier for citizen to spot police cars from behind.