Which of the following are considered standard markings for classified information?

The correct choice encompasses the standard markings that are specifically designated for classified information, which include banner markings, portion markings, and a classification authority block.

Banner markings are essential as they appear at the top and bottom of a classified document and indicate the overall classification level (e.g., "Top Secret," "Secret," or "Confidential"), ensuring that anyone who views the document is immediately aware of its classification. Portion markings, on the other hand, provide a classification level for individual sections or paragraphs within a document, which is crucial for determining the appropriate handling and dissemination of those specific portions. The classification authority block identifies the person or agency that has designated the classified status of the information, thereby establishing accountability and clarity regarding who is responsible for the classification decision.

While the other options listed contain components that might relate to classified information, they do not represent the standardized marking systems that are required by regulations for properly designating the classification levels of documents. Header and footnote markings, internal notes, summary markings, color codes, and digital signatures may have their uses but do not align with the established framework for marking classified information.