SDCL § 6-17-6: Signer's address and date of signing--Certain signatures invalid.

The signer or circulator of the petition may add the signer's place of residence and the date of signing. The signer's post office box number may be given in lieu of a street address if the signer lives within a municipality of the second or third class. A date may be written in full or may be written using standard abbreviations, including numerals. No signature on a petition is valid if signed more than one year before the filing of the petitions.