noun
policy number
Used in insurance contexts to refer to the unique identifier of an insurance policy.
保険証券に証券番号が記載されています。
The policy number is written on the insurance certificate.
保険証券 is the insurance policy document itself, while 証券番号 is the policy number printed on it.
Compound of 証券 (securities, certificate) and 番号 (number). The exact historical derivation is uncertain, but the term is straightforwardly formed from these components.