What does the license plate 'sd' mean?

[McMiguel]

sd license plates are vehicles belonging to the Equipment Department of the Shenyang Military Region, where 's' stands for Shenyang Military Region and 'd' stands for Equipment Department. White license plates are commonly seen on vehicles of national authority institutions such as public security departments, judicial departments, procuratorates, armed police forces, and the People's Liberation Army. License plates, commonly known as vehicle plates, are panels hung on the front and rear of vehicles, usually made of aluminum, sheet metal, plastic, or paper, inscribed with the vehicle's registration number, registration region, or other relevant information. License plates serve to number and register vehicles, with their primary function being to identify the vehicle's region of registration and to trace the vehicle's owner and registration details based on the plate.