Okla. Stat. tit. 59, § 725.1
Every person who writes or prints, or causes to be written or printed, his name (whether or not the word "Doctor", or an abbreviation thereof, is used in connection therewith) in any manner in connection with such person in any manner engaging in, or in any manner holding himself out as engaging in, any of the branches of the healing art as defined in 59 O.S.1951 § 702 , must append to his name so written or printed in the same size letters as his name appropriate and generally and easily understood words or letters, which clearly show and indicate the branch of the healing art in which he is licensed to practice and is engaged.
Laws 1947, HB 159, c. 16, § 1, emerg. eff. March 13, 1947.