When Street signs noticing Parking restrictions are required by state or local law, the signs shall not be placed more than 200 feet apart. The signs shall indicate by legible letters, words and figures the hours prescribed for said Parking restrictions within 100 feet on either side of the sign, except that such signs need not be placed within the boundaries of the grounds of a public institution if signs noticing the Parking restrictions within such boundaries are erected at each motor vehicle entrance to the grounds of such public institution.