Which of the following is not a common emergency signal?

The term "Affirmative" is not recognized as a common emergency signal within maritime communication protocols. In contrast, "Mayday," "Pan-pan," and "Securité" are all established distress signals used in maritime radio communications.

"Mayday" is the most urgent distress signal, indicating that a vessel or person is in a life-threatening situation and requires immediate assistance. "Pan-pan" denotes a situation that is urgent but not life-threatening, signaling that there is a problem aboard that may need attention. "Securité" is used for maritime safety messages and indicates that there is important navigational or safety information that other vessels should be aware of, but it is not an emergency in the traditional sense.

Understanding these distinctions is crucial for effective communication in emergencies at sea, where clarity can be a matter of life or death. The key takeaway is that "Affirmative" does not fit into this category of established emergency signals, which is why it is the correct answer.