Section 15. (a) A petition for the adoption or revision of a charter shall conform with the requirements of subsection (c) and shall have a sentence in substantially the following form at the top of each page:
Each of the undersigned requests that the (city) (town) of . . . . . . revise its present charter or adopt a new charter, and each of the undersigned certifies that he is a registered voter of said (city) (town) whose residence addresses at the times set forth below were as shown below, and that he has not signed this petition more than once.
(b) A petition suggesting a charter amendment under section ten shall conform with the requirements of subsection (c) and shall have a sentence in substantially the following form at the top of each page:
Each of the undersigned requests that the (city council) (town meeting) propose the charter amendment(s) attached hereto to the voters of the (city) (town) of . . . . . ., and each of the undersigned certifies that he is a registered voter of said (city) (town) whose residence addresses at the times set forth below were as shown below, and that he has not signed this petition more than once.
(c) The state secretary shall prescribe the form of all petitions under this chapter. Section seven of chapter fifty-three shall apply to all such petitions. No petition shall contain or be accompanied by any indication of party or political designation.