The Probert Encyclopaedia of Money

FRANK

A frank is the signature of a person possessing the privilege of sending letters free of postage. In Britain the privilege of giving franks for letters was enjoyed within certain limits by all peers, members of parliament, etc, until 1840, when it was abolished by the act which established the penny postage. Today a frank refers to a mechanically printed mark on a letter or parcel which provides a record that postage has been paid.
Research Frank