Your head is the only visible indicator for Search And Rescue or approaching boats.
If no one knows you’re there, it could be a long wait in cold water. Even with a flight plan, the search won’t begin until 30 minutes after the flight plan expires—and then it is by radio and telephone. Search-and-rescue forces may not be activated until three hours after your estimated time of arrival, and the search area may be quite broad. Your odds improve if you could be seen from far away or above.
Although we are hovering at low altitude while searching your chances can improve dramatically with either bright objects around you or on you! Your head and part of your shoulders are the only indicators we have.Pat O'Brian - USCG Rescue Pilot