What must a U.S. classified document containing NATO information include?

A U.S. classified document containing NATO information must include a clear identification of NATO classified information to ensure that users understand the specific sensitivities and handling requirements associated with NATO data. This identification is crucial because NATO classified information is governed by distinct standards and protocols that differ from U.S. national classifications. By clearly marking the document as containing NATO information, it assists in safeguarding the content and emphasizes the need for adherence to NATO's handling guidelines, as well as the importance of protecting allied information.

The presence of a label indicating the level of classification and a classification authority signature are specific to U.S. classification protocols but may not fully encompass the unique requirements associated with NATO information. Thus, while those elements are important for U.S. classified documents, the identifying mark for NATO is the most critical element in this context.