The office of a doctor, practitioner, dentist, minister, architect, landscape architect, real estate agent, insurance agent, stock broker, financial planner, engineer, lawyer, author, musician or other recognized trade or profession. When established in a residential district, a professional office shall be incidental to the residential occupation, not more than 25% of the floor area of one story of a dwelling unit shall be occupied by such office, and only one unlighted nameplate, not exceeding two square feet in area, containing the name and profession of the occupant of the premises shall be exhibited.