The Sign of Neptune – derived from the false god Neptune. Even today, people worship this image by asking it to “bless” newly constructed ships. So goes the long standing tradition of the Line-crossing ceremony:
“King Neptune plays a central role in the Line-crossing ceremony initiation rite still current in many navies, coast guards, and merchant fleets. When ships cross the equator, “Pollywogs” (sailors who have not done such a crossing before) receive “subpoenas” to appear before and Her Highness Amphitrite and often various dignitaries, who are all represented by the highest-ranking seamen). Some Pollywogs may be “interrogated” by King Nepture and his entourage. At the end of the ceremony — which in the past often included considerable hazing — they are initiated as Shellbacks or Sons of Neptune and receive a certificate to that effect.” – Wikipedia.