"Home occupation" means an accessory use of a service character conducted within a dwelling by the residents thereof, which is clearly secondary to the use of the dwelling for living purposes and does not change the character thereof or have any exterior evidence of such secondary use other than a small sign. The office of a physician, surgeon, dentist or other professional person, including an instructor in individual musical instruments limited to a single pupil at a time, who offers skilled services to clients, and is not professionally engaged in the purchase or sale of economic goods, shall be deemed to be home occupations. Beauty parlors, barber shops, dancing instruction, band instrument instruction in groups, tourist homes, real estate offices, insurance offices, convalescent homes, mortuary establishments, and stores, trades or business of any kind not herein excepted shall not be deemed to be home occupations. Borderline cases shall be ruled on by the Board.