It shall be unlawful for any person to park upon any street, alley or public place within the city any vehicle displayed for sale. No person shall adjust or repair any automobile or motorcycle, or race the motor of same, while standing on the public streets or alleys of the city, excepting in case of breakdown or other emergency requiring same. No person, hobbyist or employee connected with a garage or repair shop shall use sidewalks, streets or alleys in the vicinity of such garage or shop for the purpose of working on automobiles or vehicles of any description.