Which marking indicates that more information of a classified nature is present?

The choice indicating that more information of a classified nature is present is the use of portion markings. Portion markings are specific designators attached to sections of documents to indicate the classification level of that particular part. For example, when a document has multiple levels of classified information, portion markings help identify which sections contain sensitive information and at what classification level, thereby guiding the reader on how to handle that information appropriately.

In classified documents, portion markings serve to clarify the classification of different segments within the text, allowing for a more granular approach to information management. This is particularly important in ensuring that portions of a document that may be declassified can be easily identified, without compromising the integrity of the whole document.

The other options, while important within their contexts, do not specifically indicate that additional classified information exists within the document as portion markings do. For instance, the term "NOFORN" denotes that information must not be shared with foreign nationals, but it does not indicate the presence of additional classified material. Similarly, banner markings provide overall classification, while the terms "Confidential" and banner markings denote the security level but do not provide details about their contents' classification levels.