No signs shall be permitted upon any land or structure within the Professional District (P) with the exception of one sign per lot which shall bear only the name and occupation of the resident. Such sign shall have a maximum area of eight square feet and may be located on the building wall or in the front yard, provided that it is set back not less than 25 feet from any side line, that it is set back not less than 15 feet from the front lot line and that it is not more than six feet above the finished grade at its location.