Commodore Joe Redcloud wrote in
:

You are entering an unfamiliar but busy harbor at night and see a
white light flashing morse code for the letter "A". What are you
looking at, and what action, if any, should you take?


Commodore Joe Redcloud

Often referred to as the "Seabuoy", it will mark the beginning of the
entrance channel.
Technically it is a midchannel buoy, but frequently, local regs will
require you to pass it on a particular side.