serial numbered ballots
serial numbered mail in ballot sleeves
signature verification on mail in and drop box ballots
but most importantly ... the will power to throw out the fraudulent ballots. Or in other words, the enforcement of the voting laws.
No mail-in ballots. Why can't people get this through their thick skulls? No matter what mechanisms that are used to "secure" mail-in ballots, they can still be lost. You can't lose a ballot when going to an actual voting place and casting your ballot after showing your ID. If people are too damn lazy to get off their fat asses and vote in person then perhaps they shouldn't be voting. I am crippled and I still go and vote in-person.
I am sorry, but signature verification is worthless.
Photo ID is much more important and should be required if it has a check-box for verified citizenship.