Mid 19th century; earliest use found in Robert Curzon (1810–1873), traveller and collector of manuscripts. From Byzantine Greek σήμαντρον type of gong used to summon believers to worship (in modern Greek now usually σήμαντρο), specific use of ancient Greek σήμαντρον seal, sign, mark from σημαίνειν to show, signify + -τρον, suffix forming nouns of instrument.