What indicates a buoy that should be left to port when approaching from downstream?

The indication that a buoy should be left to port when approaching from downstream is represented by the use of odd numbers. In the U.S. Aids to Navigation System, buoys are marked with specific numbering systems to denote navigation channels. Odd-numbered buoys are designated as left-hand (or port) buoys when a vessel is navigating upstream. This means that when approaching from downstream, these buoys will be on the right or starboard side of the vessel, and a mariner should keep them on their left or port side as they navigate.

This numbering system is crucial for safe navigation, as it helps mariners identify their position in the channel and make appropriate navigation decisions. The usage of odd numbers for left-side buoys is a standard practice to ensure consistency and safety in waterways.