Model cars are a super fun thing to make and putting custom police decals on them can help you to have a truly special model car and a special overall look. When it comes to putting on custom decals you want to first make sure that you have the right decal for the vehicle that you are making. You want to have your decal made and ensure that it is fitted to the vehicle prior to placing it and prior to dipping it in the water.
With clear back decal paper you are going to want to put the paper in the water for a matter of seconds so that the decal can start to peel away from the backing. The decal will peel and you can then remove it from the water and remove the backing entirely. After the backing is off, you want to line up your decal and place it on the dampened side of the vehicle. You want to make sure there are no air bubbles and that the decal is lined up before it dries. After the decal dries, it will be affixed to the side of the model car.