Movable stop signs may, under supervision of the Chief of Police, be placed at any crosswalk adjacent to a school or other institution of learning one-half (1/2) hour before said school opens in the morning, five (5) minutes before school is dismissed at noon, one-half (1/2) hour before school opens in the afternoon, and five (5) minutes before school is dismissed in the afternoon. The movable stop signs shall be left standing in the streets until all of the children have entered the school or left the school. Such movable stop signs shall have painted thereon the words "Stop School Crossing" or words of similar import. (1975 Code § 8-5-12)