爪つめ印いん

noun

thumb print; nail impression

Refers to a mark made by pressing a fingernail or thumb into a surface, often used historically as a signature or seal substitute.

• 昔むかしの文もん書じょには、署しょ名めいの代かわりに爪つめ印いんが押おしてあることがある。

  Old documents sometimes have a thumb print pressed instead of a signature.