"When a person or party approaches your post, you should challenge them at a distance that is sufficient for you to react if they turn out to have hostile intentions. You should say in a firm voice, loud enough to be easily heard, "Halt! Who goes there?" (or "Who is there?"). Once the person answers, you should then say "Advance to be recognized." ... If you have identified the person or persons approaching, permit them to pass. If you are not satisfied with that person's identification, you must detain the person and call the petty officer of the watch."
— 11th General Order of the US Marine Corps