23 C.F.R. § 750.105
Signs that may be permitted in protected areas
(a) Erection or maintenance of the following signs may be permitted in protected areas:
Class 1—Official signs. Directional or other official signs or notices erected and maintained by public officers or agencies pursuant to and in accordance with direction or authorization contained in State of Federal law, for the purpose of carrying out an official duty or responsibility.
Class 2—On-premise signs. Signs not prohibited by State law which are consistent with the applicable provisions of this section and § 750.108 and which advertise the sale or lease of, or activities being conducted upon, the real property where the signs are located.
Not more than one such sign advertising the sale or lease of the same property may be permitted under this class in such manner as to be visible to traffic proceeding in any one direction on any one Interstate Highway.
Not more than one such sign, visible to traffic proceeding in any one direction on any one Interstate Highway and advertising activities being conducted upon the real property where the sign is located, may be permitted under this class more than 50 feet from the advertised activity.
Class 3—Signs within 12 miles of advertised activities. Signs not prohibited by State law which are consistent with the applicable provisions of this section and §§ 750.106, 750.107, and 750.108 and which advertise activities being conducted within 12 air miles of such signs.
Class 4—Signs in the specific interest of the traveling public. Signs authorized to be erected or maintained by State law which are consistent with the applicable provisions of this section and §§ 750.106, 750.107, and 750.108 and which are designed to give information in the specific interest of the traveling public.
(b) A Class 2 or 3 sign, except a Class 2 sign not more than 50 feet from the advertised activity, that displays any trade name which refers to or identifies any service rendered or product sold, used, or otherwise handled more than 12 air miles from such sign may not be permitted unless the name of the advertised activity which is within 12 air miles of such sign is displayed as conspicuously as such trade name.
(c) Only information about public places operated by Federal, State, or local governments, natural phenomena, historic sites, areas of natural scenic beauty or naturally suited for outdoor recreation and places for camping, lodging, eating, and vehicle service and repair is deemed to be in the specific interest of the traveling public. For the purposes of the standards in this part, a trade name is deemed to be information in the specific interest of the traveling public only if it identifies or characterizes such a place or identifies vehicle service, equipment, parts, accessories, fuels, oils, or lubricants being offered for sale at such a place. Signs displaying any other trade name may not be permitted under Class 4.
(d) Notwithstanding the provisions of paragraph (b) of this section, Class 2 or Class 3 signs which also qualify as Class 4 signs may display trade names in accordance with the provisions of paragraph (c) of this section.