A ballot is sent to each registered voter and it can't be forwarded. Voter registration rolls are purged by the registrar. The voter must sign the ballot using the same signature as on the voter registration. Any registered voter may challenge a ballot or a registration.
So you're saying they don't know unless someone happens to get the signature verified. Sounds a bit flaky to me.
The signature on all ballots are checked. The first step in processing is to checked the signature on the outside of envelope against the signature on file in the voter registration record to make sure they match. If they do not match, the ballot is not processed and returned to the voter. Any registered voter may visit the county registrar's office to watch ballot processing.
Unlike election day voting where ballots must processed in just hours, most mail ballots are received a number days before election day allowing more time for processing.