Within sixty days after the enactment by the council of any ordinance authorizing the issuance of bonds, notes or other evidence of debt the repayment of which requires a pledge of the full faith and credit of the county, or requires the approval of the issuance of bonds by a public service district within the county a petition signed by qualified electors of the county equal in number to at least fifteen percent of the qualified electors of the county, or if such ordinance relates to a bond issue for a public service district, fifteen percent of the qualified electors of the district may be filed with the clerk of the county council requesting that any such ordinance be repealed; provided, however, that this section shall not apply to bond issues approved by referendum or to notes issued in anticipation of taxes.