A single written sign, and the settled nature of a person. Both are what a thing is recognisable by.
Greek kharakter (a stamping tool, an engraved mark), from kharassein (to sharpen, to engrave, to scratch); the settled-nature-of-a-person sense grows from the idea of a mark stamped in and not easily erased.
A single written sign, and the settled nature of a person — both are what a thing is recognisable by, stamped in rather than merely worn.