A sign by which to be recognised, i.e. the heraldic badge or emblem or *crest worn by the retainers of a particular lord, or noble house; part of the *livery. Before *heraldry became an art and science, knights would put signs or simple cognisances on their shields as an easy means of identification in battle or *melee.
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.