California Code, Business and Professions Code - BPC § 5491.2

(a) A city or county may impose reasonable fees upon all owners or lessees of on-premises business advertising displays for the purpose of covering its actual cost of inventorying and identifying illegal or abandoned advertising displays which are within its jurisdiction.  A city or county may exempt from the payment of these fees the owner of a display identifying an achievement award, the name of a farm, or the name of a business for which the farm produces, if the display is located on an operating farm within an agricultural preserve established pursuant to the Williamson Act (Chapter 7 (commencing with Section 51200) of Part 1 of Division 1 of Title 5 of the Government Code), and if the city or county finds that the exemption will further the purposes of the agricultural preserve.

(b) The actual cost to the city or county may be fixed upon a determination of the total estimated reasonable cost.  The amount of that cost and the fee to be charged is exclusively within the discretion of the city or county.