If any of you are wondering what the knotted rope is called, it's a Quipu. Iirc it was used by the Inca or Peruvian people. The distance between each knots and the "direction" of each knot combines into the intended message. Multiple Quipus would be lined up in the intended sequence on a piece of durable material (leather, stick) and worn by the courier-runner as a necklace. Been a while since I saw it in the CMB manga years ago.