What is the MINIMUM required marking for a document containing CUI?

Per DoDI 5200.48, Controlled Unclassified Information (CUI), the minimum marking requirement is that the word “CUI” must appear in the header and footer of each page of a document containing CUI. Additional markings such as portion markings or cover sheets may be applied depending on the situation, but the minimum baseline requirement is header and footer placement of "CUI".

Reference Documents:

DoDI 5200.48,Controlled Unclassified Information (CUI)