According to Ford's VIN guides, the 5,6,7 digits for the Explorer police are K8A (AWD PIU). In 2013, they also made a K7A FWD version.
Basically, K in the 5th position indicates Explorer, 7/8 for a 6th position indicates whether its FWD or AWD, and the "A" in the context of an Explorer is the designation for the PIU "trim level".