Something that leads to something else. It may be an arbitrary or conventional sign that has a connection with what is signified only by agreement among people, as a flag symbolizes a nation. Or it may be a pure sign that leads to the knowledge of something without itself being first known, as our ideas lead to the knowledge of real objects. Instrumental signs give meaning or understanding, as words lead to the knowledge of things and of mental status. Manifestative signs show the existence of something else, as a person's external behavior indicates his or her personality and training.
Each of these types of signs may be either natural or supernatural depending on whetehr its basis is founded on natural reason or divine revelation.
The whole of the Church' liturgy is built on the function of word, action, and object signs as symbols of the sacred. But among the sacred signs the most important are the sacraments, which not only manifest the special presence of God but actually confer the grace they signify. (Etym. Latin signum, mark, sign, characteristic.)