The electors shall have power to propose any ordinance, except an appropriation ordinance, and to adopt or reject the same at the polls, such power being known as the initiative. Any proposed ordinance may be submitted to the Council by petition which, to be sufficient, shall be signed by electors of the City equal in number to at least ten percentum (10%) of those who voted at the last regular municipal election. All petition papers circulated with respect to a proposed ordinance shall be uniform in character and shall contain the proposed ordinance in full.