What must all classified correspondence contain for proper identification?

All classified correspondence must contain a serial number for proper identification. The serial number serves as a unique identifier that allows the Marine Corps to track and manage classified documents efficiently. This unique identification system is crucial for maintaining security, ensuring accountability, and facilitating effective retrieval of documents when needed.

Tracking numbers, code numbers, and ID numbers may serve different purposes but do not specifically denote the unique classification status and handling requirements associated with classified correspondence. The serial number is an established standard for classified documentation, ensuring that it is distinctly recognized throughout the handling and processing procedures.