The correct answer is the distress signal comprised of the International Code Flag 'N' over 'C', which specifically indicates that the vessel is abandoning ship. This signal is universally recognized in maritime communication as a clear and unambiguous message that crew and others nearby should understand the vessel is in a state of emergency and that its crew is preparing to evacuate.
The combination of Flags 'N' (for "No") and 'C' (for "Yes") effectively conveys the critical situation of abandoning the vessel, aligning with international maritime signal conventions. Therefore, when these flags are displayed, it's a strong visual signal for other vessels and nearby individuals to be on alert and ready to assist if needed.
Other options do not convey the same level of specificity regarding abandonment. For instance, the International Code Flag 'A' is related to the status of being in the water or a diver's indication, while sound signals like continuous horn blasts or short blasts may signal distress but do not specifically indicate that the vessel is being abandoned. Therefore, the use of Flag 'N' over 'C' is the appropriate and correct choice for signaling an abandonment situation at sea.