The fly has 7 alternating blue and white stripes (4 blue and 3 white) which symbolize the seven seas. 

At the hoist, surrounded by a red field, on a white background is a sketch of a sentry box encircled by a rudder. The sentry box is a reproduction of the famed Devil's Sentry Box ( garita del diablo ) which borders the ancient sea walls of historic San Felipe del Morro, San Juan's centurias old spanish forres. Numerous legends have been meshed around the lonely watch of the sea lanes leading to the San Juan harbor. 

The rudder encircling the sentry box symbolizes the San Juan Power Squadron's dedication to the arts and science of piloting, seamanship and navigation. San Juan