On all cards, books, papers, signs or other written or printed means of giving information to the public, used by those licensed by this chapter to practice chiropractic, the practitioner shall use after or below his or her name the term chiropractor, chiropractic physician, D.C., or D.C.Ph.C., designating his or her line of drugless practice, and shall not use the letters M.D. or D.O.: PROVIDED, That the word doctor or "Dr." or physician may be used only in conjunction with the word "chiropractic" or "chiropractor". Nothing in this chapter shall be held to apply to or to regulate any kind of treatment by prayer.