CMMC Practice MP.3.122: Mark media with necessary CUI markings and distribution limitations.
CMMC CLARIFICATION (Ref CMMC – Appendix B)
All media (e.g., USB drives, CDs, DVDs, diskettes, hard drives, and paper) must be properly marked to alert individuals to the presence of Controlled Unclassified Information (CUI)stored on the media. Since the media itself may be small and provide limited space to mark it you should at a minimum mark it as “Controlled” or CUI” and the designating agency. If the media is hard to mark alternate methods may be approved to indicate the presence of CUI. For example, a company may place a CUI banner on the desktop background image or monitor attached to the system. They could also require the user to accept a banner message stating CUI may be present on the system.