I have always worried if I'm running around in some port and something happens to me. If the ship has my passport and goes sailing off while I'm in some hospital, Could be a mess. Depends on what country your in.

When I was a little kid I was taught always leave your passport and wallet in your front pants pocket. When in a crowded place rest your thumb on them as you walk and be aware of anyone close to you. Never show wealth. My Father's old belief was never look like an American, an impossible task for him.