The identification codes are not located on the rear end, but rather inside the door or glove box. The exact location of each number depends on the make and model of the vehicle.
The identification codes used to describe the rear end or axle of a vehicle are called RPO codes. On standard GM vehicles, the RPO codes follow a simple format. They use the letters F, G or H, which are then followed by two characters. However, if the vehicle is modified in any way, the letters may not be present.
If the letters cannot be found inside the door sticker, the glove box also usually has the code printed somewhere in it.