Maryland Code, Public Safety § 13-202

(1) citizens of the State;

(2) citizens of the United States who take an oath of allegiance to the State; or

(3) of foreign birth and who:

(1) is exempted by the laws of the United States;

(2) is exempted by the laws of the State;

(3) is a member of a regularly organized fire or police department in a county, city, village, or town;

(4) is a judge or clerk of a court of record;

(5) is a register of wills and deeds;

(6) is a sheriff;

(7) is a member of the clergy;

(8) is a practicing physician;

(9) is a superintendent, officer, or assistant of a hospital or correctional facility;

(10) has been judged mentally incompetent;

(11) is addicted to narcotic drugs; or

(12) has been convicted of an infamous crime.