[zeugma]

They say the number is for facilitating audits. But the only legitimate audit is of who votes. Audit the hell out of -who- voters are, that is fine. But you do not need ballots to do that, just voter attendance rolls. Audit the hell out of participants who showed up. And match that number against the number of ballots that were cast.

Not really necessarily for removing secrecy. Ballots are printed either beforehand, or on demand. In either case, you have a few ballots fanned out and the voter randomly chooses one. That way, the ballots themselves may very well be serialized to facilitate audits. i.e., you know that ballot #332 was cast in this particular polling location, but you don't know who actually filled it out.

[Engedi]

When I vote in Michigan, I fill out my voting card name, address and sign it. This is after I present my driver’s license which is scanned and confirmed I’m in the right place.

Then a person takes my registration card and passes it to another person who writes the ballot number on the card and then hands me a ballot after they have ripped the top off of the ballot that has numbers on it. There are no ballots just laying on the table to pick from. Interesting.