California Code, Business and Professions Code - BPC § 14411

The filing of any fictitious business name statement by a person required to file such statement pursuant to Section 17910 shall establish a rebuttable presumption that the registrant has the exclusive right to use as a trade name the fictitious business name, as well as any confusingly similar trade name, in the county in which the statement is filed, if the registrant is the first to file such a statement containing the fictitious business name in that county, and is actually engaged in a trade or business utilizing such fictitious business name or a confusingly similar name in that county.

The rebuttable presumption created by this section shall be one affecting the burden of producing evidence.