California Code, Business and Professions Code - BPC § 5405.5

In addition to those displays permitted pursuant to Section 5405, displays erected and maintained pursuant to regulations of the director, which will not be in violation of Section 131 of Title 23 of the United States Code, and which identify the location of a farm produce outlet where farmers sell directly to the public only those farm or ranch products they have produced themselves, may be placed or maintained within 660 feet from the edge of the right-of-way so that the copy of the display is visible from a highway.

The advertising displays shall indicate the location of the farm products but not the price of any product and shall not be larger than 150 square feet.