Which of the following is the most recognizable international signal for distress?

The most recognizable international signal for distress is the signal that consists of one loud horn blast. This signal is universally understood as a way to convey an emergency situation that requires assistance. It is designed to capture attention quickly and effectively, making it ideal in various environments, whether on land or at sea.

The loud horn is clear and penetrating, making it effective in multiple conditions, including noisy settings where other signals might go unnoticed. While other options may relate to signaling distress, they are less universally recognized or may not convey urgency as effectively as a single, loud horn blast.