circlet vs signet ring

circlet

noun
  • A ring (typically of gold or silver) worn as an ornament on the head. 

  • A round body; an orb. 

  • A crown without arches or a covering. 

  • A small circle. 

signet ring

noun
  • A finger ring bearing a signet, seal or coat of arms. 

How often have the words circlet and signet ring occurred in a corpus of books? (source: Google Ngram Viewer )