fair surfing conditions at San Francisco - Ocean Beach

I have a question about shark sighting etiquette. Was out back this evening when a set came through. Shoulder high, not so clean. I paddled over the first wave hoping for something better on the next. Straight ahead I saw the shadow of a shark in profile as the wave moved over it. The sun was setting, hence the wave was illuminated cleanly from behind. It was super clear. I would say at least 10 feet in length. I realized it wasn't a Whitey as the proportions were too elongated. It also looked brownish and the dorsal fin was lazy. It moved very slowly in profile, almost still, and then turned towards the beach, then disappeared. I convinced myself it was a Basking shark (which it probably was) so not much to panic about. I still caught that wave in though and paddled to another peak. There were still a few guys out but no one else saw it. So .... I kept this event to myself. I have lived/surfed in South Africa/Oz and elsewhere where sharks are a regular occurrence and people keep quiet and calm... unless it's a beast of a Whitey. Are there rules here for such things? My conscience is playing on me. Do surfers here really shout out 'Shark!' in the line up?