Hidden Object scenes are those that task you with gathering a list of items from a mess of junk. There are several of these scene throughout the game, the first of which is inside the helicopter after giving Hawk the medkit. For this achievement, just do not use the Hint button. These is no time limit and the objects are usually not that well hidden. Look carefully. This is only missable in the sense that if you don't do it in your playthrough, you will have to delete your first save and start a new save for about 2 minutes.