Abraham Lincoln. The country’s 16th president is known for many things: Signing the Emancipation Proclamation. Appearing on the $5 bill. Helping to usher in the modern-day practice of mail-in voting. Not familiar with that last one? UNLV professor Michael Green to the rescue! He’s a historian who specializes in the Civil War era, which is right around the time mail-in ballots became a prominent piece of U.