At least 30 days' notice of the referendum shall be given by proclamation of the mayors of the cities, boroughs or incorporated towns, by the chairmen of the boards of county commissioners, by the presidents of the boards of township commissioners or by the chairmen of the boards of township supervisors, as the case may be. A copy of the proclamation shall be posted at each polling place of the municipalities on the day of the election and shall be published once in at least one newspaper of general circulation in the municipalities during the 30-day period prior to the election.