I am not a RE professional yet, so don't take my word for it, but I do believe that in California, you need a license. Here's some info from the California Department of Real Estate:
"This license is required of individuals who conduct licensed real estate activities as described in the Real Estate Law under the supervision of a licensed broker. A license may also be obtained by a person who does not immediately intend to be employed by a broker. However, a salesperson without an employing broker may not perform acts requiring a real estate license."
Check the DRE website for more info. I think I don't have enough posts to add a link yet, but just google for it. Or piece it together from the next line:
www . dre . ca . gov / exm_sales.html