Whenever standards relating to kind, class, quality, or condition of grain are effective under section 76 of this title for any grain no person shall in any sale, offer for sale, or consignment for sale, which involves the shipment of such grain in interstate or foreign commerce, describe such grain as being of any grade in any advertising, price quotation, other negotiation of sale, contract of sale, invoice, bill of lading, other document, or description on bags or other containers of the grain, other than by an official grade designation, with or without additional information as to specified factors: Provided, That the description of such grain by any proprietary brand name or trademark that does not resemble an official grade designation, or with respect to interstate commerce, by the use of one or more grade factor designations set forth in the official United States standards for grain, or by other criteria shall not be deemed to be a description of grain as being of any grade.