From the article in 2012
"On the morning of the primary here in August, the local elections board met to decide which absentee ballots to count. It was not an easy job. The board tossed out some ballots because they arrived without the signature required on the outside of the return envelope. It rejected one that said “see inside†where the signature should have been. And it debated what to do with ballots in which the signature on the envelope did not quite match the one in the county’s files. “This ‘r’ is not like that ‘r,’ †Judge Augustus D. Aikens Jr. said, suggesting that a ballot should be rejected. Ion Sancho, the elections supervisor here, disagreed. “This ‘k’ is like that ‘k,’ †he replied, and he persuaded his colleagues to count the vote."
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That board was correctly validating mail-in ballots. The Election Code has instructions how to validate a mail-in ballot. If there are not two signatures - one on the application and one on the envelope with the ballot inside, it is rejected. However, if the two signatures do not match, the board can get the original application of the voter when he/she became a voter and that signature can be compared to the two or to the one signature if there is only one on the ballot materials.
The Judge of that board should know how to validate all information required and present that to the Board. Once all evidence is presented, the board votes to accept that ballot or not based on signatures.
One more thing:
The ballot itself is in a sealed envelope and no one on the board opens that envelope. If someone did open that envelope, the person who opened it could see how that particular voter voted because that person has the name of that voter in front of him/her. That is not allowed. Once there is a stack of ballot envelopes so no one could know how anyone voted (no name is on that ballot envelope), ballot envelopes are sent to be counted in machines in Central Counting.