(a) In examining any petition required or permitted to be signed by landowners, the county clerk or district secretary shall disregard the signature of a person not shown as owner on the assessment roll unless prior to certification the secretary or county clerk is furnished with written evidence, satisfactory to the county clerk or district secretary, that the signer:
(i) Is a legal representative of the owner;
(ii) Is entitled to be shown as owner of land on the assessment roll; or (iii) Is a purchaser under a contract to purchase real property.