Each petitioner signing such petition shall write or cause to be written opposite to his name on said petition, the name of the city and ward in which he then resides, if he resides in a city, or if he does not reside in a city, then the name of the precinct or township in which he resides at the time of signing such petition; and no person shall sign such petition unless he shall be, at the time, a legal voter in said county at general elections.