What document must observers sign during their briefing?

The correct choice is the Memorandum for Observers. This document serves as an official record that outlines the responsibilities and expectations placed upon observers during a briefing. By signing this memorandum, observers confirm that they understand their role in the observation process and agree to adhere to the specified protocols.

This memorandum typically includes important information related to the observer's duties, such as confidentiality, impartiality, and the ethical considerations they must maintain while observing testing or other activities. Therefore, the signature serves as an acknowledgment of these critical elements, ensuring that observers are fully informed of their responsibilities and the importance of maintaining integrity in their role.

Other options may refer to agreements or guidelines that do not specifically serve as the formal acknowledgment required for observers. While they might be relevant to the broader context of testing and conduct, they do not fulfill the same purpose as the Memorandum for Observers.