Special signage shall be permitted with the permission of the Planning Board. Applications for special signage shall be reviewed in light of reasonable standards relating to size, scale, illumination, safety, duration, maintenance, location and design harmony. Factors to be considered by the Board shall include, but not necessarily be limited to, marketing impact, compatibility with surrounding uses and structures, and compatibility with other signage in the immediate area and in the zoning district in which the special signage will be located.