What does three short blasts of a whistle or horn signify?

Three short blasts of a whistle or horn is a universally recognized distress signal that indicates the vessel is backing up. This communication method is crucial for the safety of navigation, particularly in crowded or confined waters where vessels need to be highly aware of each other's movements. When a vessel issues three short blasts, it effectively communicates to nearby operators that it is in the process of reversing, allowing other vessels to take appropriate action to avoid collisions. This helps maintain safety and prevent misunderstandings about the intended movement of the vessel. Understanding these signals is essential for mariners, as they facilitate safe interaction between vessels in various situations.