Every Yacht Club has their own unique Burgee that identifies their mambers's boats.
According to Chapman Piloting, "A burgee is a triangular, rectangular or swallowtailed flag denoting club or squadron membership."

The etiquette on how to fly your Burgee depends on your type vessel.
Modern sailing vessels fly the Burgee from a lanyard under the starboard spreader on the mast, and older sailing vessels fly the Burgee from the main masthead.
Power boats fly the Burgee off a short staff on the bow.