The notes had 150 minor marks that acted as security measures to identify forgeries. These were often assumed to be printing errors, and were changed between issues of notes.[n 1] Each note bore an alphanumeric serial designation and the signature of the Chief Cashier of the Bank of England.[5] Prior to the release of any notes by the Bank of England, all serial numbers were recorded in ledgers so the bank could verify its liabilities; these numbers were checked when the notes circulated back through the bank.[6][n 2]