Each bond or other evidence of indebtedness shall contain on its face a statement specifying the purpose for which the same is issued and it shall be unlawful for any officer of the city to use the proceeds thereof for any other purpose, except that whenever the proceeds of any bond issue, or any part thereof, shall remain unexpended and unencumbered for the purpose for which said bond issue was made, the Council may authorize the use of such unexpended and unencumbered funds for the retirement of such bond issue, or if such bond issue shall have been fully retired or if any of such funds remain after such retirement, then for the retirement of other bonds or obligations of the city. All bonds and other evidences of indebtedness issued by the city shall be signed by the Mayor and countersigned by the Treasurer, under the seal of the city. Interest coupons may be executed with the facsimile signatures of the Mayor and Treasurer. A complete and detailed record of all bonds and other evidences of indebtedness issued by the city shall be kept by the Clerk. Upon the payment of any bond or other evidence of indebtedness, the same shall be marked “Cancelled.” Any officer who shall violate the provisions of this section shall be deemed guilty of misconduct in office. No cancelled bond shall be destroyed until ten (10) years have elapsed following its final retirement date.