signet
/ˈsɪgnɪt/noun
1- historical a small seal, especially one set in a ring, used instead of or with a signature to give authentication to an official document〈史〉戒指图章; 小图章; 小公章。
1.1
- （一般作the Signet）the royal seal formerly used for special purposes in England and Scotland, and in Scotland later as the seal of the Court of Session（旧时英格兰和苏格兰的）玉玺; （苏格兰最高民事法庭的）官印。
词源
late Middle English: from Old French， or from medieval Latin signetum, diminutive of signum 'token， seal'.