"Switching on your PvP flag makes it possible for you to fight other PvP-flagged players in the Open Sea, even while not within a PvP Hotspot. Any player may attack a foreign player who has the PvP flag set. Flagging yourself indicates that you are willing to fight any and all opponents. You may change your PvP flag status at any Port Captain."
With the PvP flag enabled through this mission, hostile NPC groups will not attack you and you gain a speed boost on the Open Sea.