Which of the following are examples of sign/countersign?

• A. Code words, challenge/password, number combinations, recognition signals.
• B. Biometric data only.
• C. Public announcements.
• D. Hand signals and written notes.

Answer: (A)

Sign and countersign rely on a two-part check where one party provides a prompt or signal and the other responds with the correct agreed response to prove authorization. The best set of examples covers a variety of prompt-and-response methods that partners can use without exposing the exchange to outsiders. Code words function as the agreed cue that signals membership or intent; the corresponding countersign is the specific reply that confirms it. A challenge with a password illustrates a direct prompt-and-response flow: the challenge is the prompt, the password is the response that validates the holder’s knowledge. Number combinations work the same way, where a numeric prompt requires the correct numeric response. Recognition signals are prearranged cues that only trusted teammates understand and acknowledge, completing the mutual verification when the proper response follows.

Biometric data by itself is a static factor used for identification or verification, not a dynamic sign/countersign exchange. Public announcements are open to anyone and do not provide the private mutual verification that sign/countersign systems rely on. Hand signals and written notes can be part of signaling, but without a defined paired response, they don’t complete a sign/countersign interaction on their own.