@Renee HarrisHere is a statement from the Bureau of Real Estate in California.
Disclosure of Licensed Status in Advertising 10140.6. (a)
"A real estate licensee shall not publish, circulate, distribute, or cause to be published, circulated, or distributed in any newspaper or periodical, or by mail, any matter pertaining to any activity for which a real estate license is required that does not contain a designation disclosing that he or she is performing acts for which a real estate license is required."
Being as though a real estate license is not required to solicit for the wholesale of a property, it seems to me that based on laws where you reside in California, you may not have to disclose your license in your LETTER unless you are providing the property owner with the option to list their property for them (which does require a license). My suggestion was that you don't have to disclose in your LETTER, but you can disclose your status once a homeowner has CONTACTED YOU DIRECTLY to express interest. To be absolutely sure, you should consult your broker who would be well versed in matters concerning California's real estate laws specifically.