The PvP flag indicates whether or not you can engage or be engaged in PvP combat by a player of an opposing faction. If it is up, you are open for combat against the opposite faction. If it is not, you cannot be attacked by a player of an opposing faction. The PvP flag can be seen in the top corner of the screen next to your players portrait. You may see File:Horde 15.png or File:Alliance 15.png next to your portrait depending on your faction. If the icon appears, then your flag is up. If it does not, your flag is down. If your flag is temporary, the time that it will be up, will be displayed. That is, as long as you are not in contested territories, not in PvP combat, and not having quests in your log that flags you for PvP. PvP flag timers of other players are not displayed.