The county clerk shall number county, city and district measures consecutively and shall not repeat any number in any subsequent election. For each election, the numbers assigned shall begin with the number after the last number assigned under this section at the previous election. The measures shall be assigned numbers in the order in which the measures are filed with the clerk and in a manner that will not confuse county, city or district measures with state measures. The number assigned to each county, city and district measure shall be preceded by a unique county prefix number. The Secretary of State by rule shall assign a prefix number to each county for the purpose of carrying out the provisions of this subsection.