Allow players to send up a distress signal that informs everyone of their location (marks them on the map and visible from a long way off) and indicates that they are in trouble and need assistance.
There's no guarantee that those who respond, will actually be there to help (maybe they're just there to prey on the vulnerable), or that those who sent up the distress signal are actually in need of assistance (trap?). Both using, and responding to it, would be a risk.
This could be a fun way to find and form alliances (e.g. you get into trouble and someone comes to help you), but could also create opportunities for deception, setting traps, and generally being more pirate.
One way or another, if you respond to a distress signal (either with good, or bad intentions) something interesting is likely to happen.
