Any violation expressly declared to be punishable, in the discretion of the court, by either a fine, or by a fine or imprisonment, or both, shall become an infraction for all purposes under any of the following circumstances:
(a) Where a judgment imposes a punishment of a fine not exceeding $50 in the case of a first offense; or
(b) When the court grants probation to a defendant without the imposition of a sentence and, at the time of granting probation, or on application of the defendant or probation officer thereafter, the court declares the offense to be an infraction; or
(c) When the City Attorney or any deputy district attorney files in a court having jurisdiction over misdemeanor offenses a complaint specifying that the offense is an infraction.
(3-12/90 § 1.01.220)