Titulus (Latin "inscription" or "label", the plural tituli is also used in English) is a term used for the labels or captions naming figures or subjects in art, which were commonly added in classical and medieval art, and remain conventional in Eastern Orthodox icons. In particular the term describes the conventional inscriptions on stone that listed the honours of an individual[1] or that identified boundaries in the Roman Empire. A titulus pictus is a merchant's mark or other commercial inscription.
The sense of "title", as in "book title", in modern English derives from this artistic sense, just as the legal sense derives from plainer inscriptions of record.[2]