The Ida County sheriff shall have authority to declare any street or part thereof a play street and to place appropriate signs or devices in the roadway indicating and helping to protect the same. Whenever authorized signs are erected indicating any street or part thereof as a play street, no person shall drive a vehicle upon any such street or portion thereof except drivers of vehicles having business or whose residences are within such closed area, and then any said driver shall exercise the greatest care in driving upon any such street or portion thereof.