They were originally documents or licenses issued by local shugo and jito (military governors and manor stewards), but they were thought to have a mysterious meaning by the common people of the time who could not read or write, and this meaning has remained until today.
本来は地方の守護・地頭の出した書面や許可証であった物が、文字の読めない当時の民衆にとっては不思議な意味を持つ物となり、現在に至る。