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.
MD does NOT stand for medical doctor, although that's the common interpretation. MD is a Latin abbreviation, Medicinae Doctor. Its English translation is Doctor of Medicine. Similarly, a PhD stands for Philosophiae Doctor, or Doctor of Philosophy, not Philosophical Doctor. We don't use Latin much anymore, so we assign the letters a reasonable English equivalent medical doctor.