The provisions of section three of this article shall not apply to the following: (a) Directional and other official signs and notices required or authorized by law, including, but not limited to, signs and notices pertaining to natural wonders, farm wineries, mini-distilleries, scenic and historical attractions, which such signs and notices shall conform to standards respecting lighting, size, number, spacing and such other appropriate requirements as may be designated and specified by the Secretary of Transportation of the United States: Provided, That the Commissioner of Highways shall not establish any standards respecting lighting, size, number, spacing and other appropriate requirements which are stricter than such standards designated and specified by the Secretary of Transportation of the United States; (b) signs, displays and devices advertising the sale or lease of property upon which they are located; and (c) signs, displays and devices advertising activities conducted on the property on which they are located, including markers of underground utility facilities.