Final answer:
A buoy that should be left to port when entering from seaward is indicated by a nun shape in the U.S. Aids to Navigation System.
Step-by-step explanation:
In the U.S. Aids to Navigation System, a buoy that should be left to port when entering from seaward is indicated by a nun shape. A nun buoy is cylindrical in shape and is often painted red, with even numbers displayed on it. It is used to mark the right side of a channel or fairway, and is typically found on the starboard side of a vessel.