It is a military expression, which extended to popular usage, where it took several interpretations. One that matches the original is that of "password", a word used to recognize an ally or a person authorized for an entry; and it is that in Spain the Christian soldiers consulted a stranger or someone who could not distinguish in the dark with the saint of the day, and he had to respond with the sign chosen for that same day by his superiors, which was always an arbitrary word, informed only to whoever was authorized to pass. In another case it is synonymous with "representative", of something or someone who is recognized by a group of admirers or peers. It is also used to express that "everything was said about a matter", although in reality it is "up to the holy and sign", because it was said even what was secret. See shibboleth, and since we are, shibboleet, santoral.