In the trial of a defendant for violation of the provisions of sections 624.30 to 624.33, knowledge or reason to believe, within the meaning thereof, shall be deemed to exist upon the presentation of proof to the court that any county attorney, sheriff, or chief of police in the state, or a deputy or delegate of such officer, has given written notice to the defendant that tokens, checks, or slugs of the kind manufactured, sold, offered for sale, advertised for sale, or distributed by the defendant are being used in substitution for lawful coin in the operation of any such coin receptacle or machine; provided that such notice shall have been given prior to the time of the manufacture, sale, offering for sale, advertising for sale, or distribution of such tokens, checks, or slugs for which the defendant is being tried.