As head of the executive branch, the president must appoint the top officials for all of the federal agencies. These positions are listed in the Plum Book which outlines more than 7,000 appointive positions in the government.
1 When you have a Ph.D., sign your name either as Dr. Ernest Smith or Ernest Smith, Ph.D. 2  If you have a Ph.D. you should engrave all your personal envelopes or labels with either Dr. Ernest Smith or Ernest Smith, Ph.D.his is the teaching of St. Thomas Aquinas in his Treatise on Justice. (Question 58). Therefore, one should address a person with a doctorate by his title, and the person should have no fear in calling himself or herself by that name.
Quick Answer. The letters after a doctor's name indicate the advanced degree program the doctor completed, according to About.com. The most common letters are M.D. for medical doctor and Ph.D. for doctor of philosophy.