There will be markers up to a certain distance. Beyond that distance, you either have to rely on eyesight or Tactical Warning System (TWS) inventory item (yes, you have to buy it) which immediately gives you the direction/location that a shot (that hit you) came from.
If some guy is sniping you from a mile away, you won't stand a prayer of a chance. Which is why you shouldn't be standing around gazing at the scenery.
good because I always hated how in battlefield people would just spam the mark button to find people who were like so far away you could barely see them with a sniper scope.