Automatic changeable copy signs shall be authorized for all nonresidential principal structures for walls or frontage bordering or facing Main Street as an accessory to and part of the sign area of a freestanding sign, where freestanding signs are otherwise authorized in this part, and shall not exceed 50% of the authorized sign area; and where not authorized, may be placed as a wall sign not to exceed 50% of the area available, as per this part, for use as wall signage. Automatic changeable copy signs shall display only amber colored lettering or numerals on a black background advertising products sold or services provided on site. Additionally, each message shall take no more than one second to complete its display such that no animation or impression of movement is created. Each message display shall begin to change more than once every five seconds.