Section 2. Notwithstanding the provisions of chapter ninety-three, no outdoor advertising shall be erected or maintained within six hundred and sixty feet of the nearest edge of the right-of-way and visible from the main travelled way of a highway in the interstate or primary systems except the following:
(a) Directional and other official signs and notices, which signs and notices shall include, but not be limited to, signs and notices pertaining to natural wonders, scenic and historic attractions, as required or authorized by law or by the department, and which conform to standards promulgated by the secretary under Title 23 of the United States Code.
(b) Signs, displays and devices advertising activities conducted on the property upon which they are located.
(c) Signs, displays and devices advertising the sale or lease of property upon which they are located.
(d) Signs, displays and devices which are located in areas which are zoned industrial or commercial under authority of law and which have permits issued under the provisions of section three.
(e) Signs, displays and devices which are located in unzoned commercial or industrial areas which areas shall be determined from actual land use and defined by regulations to be promulgated by the department and which have permits issued under the provisions of section three.
(f) Signs lawfully in existence on October twenty-second, nineteen hundred and sixty-five and lawfully maintained thereafter, determined by the department in consultation with the board subject to the approval of the secretary, to be landmark signs, including signs on farm structures or natural surfaces, of historic or artistic significance, the preservation of which would be consistent with the purposes of this section, and which have permits issued under the provisions of section three.