It shall be unlawful for any person to wilfully or maliciously remove, destroy, mutilate or alter the number of any bicycle frame licensed pursuant to this chapter. It shall also be unlawful for any person to remove, destroy, mutilate or alter any license plate, seal or registration card during the time in which the license plate, seal or registration card is operative; provided, however, that nothing in this chapter shall prohibit the police department from stamping numbers on the frames of bicycles on which no serial number can be found, or on which the number is illegible or insufficient for identification purposes. (Ord. 209 § 5, 1955)