The petition for election provided for in Section 29712 shall be signed by voters within any public agency, or portion thereof, included within the boundaries of the territory proposed to be annexed equal in number to at least 10 percent of the registered voters residing within such public agency, or portion thereof. The petition may include one or more documents, but each document shall contain the affidavit of the party who circulated it certifying that each name affixed thereto is the true signature of the person whose name it purports to be.