Here is something that has been rattling around in my head for a bit.

I am in California. During the last primary election I took my mail in ballot in to the actual polling place and had a rather interesting conversation with a poll worker.

After finding the right table I showed my driver's license, ostensibly to make it easier for them to get the spelling of my name right when looking it up. While waiting for them to find me in the printout I offered my blank mail in ballot and said that it was my understanding I was supposed to turn it in to vote there. At this point another, I assume senior, poll worker came up and said that I could just fill out the mail in ballot and put it into a specific box in the middle of the room, after signing and sealing it etc. This would then be taken to the county offices to be counted. I asked why I couldn't just run it through what I assumed was a machine sitting nearby and was told there weren't any machines on site, just boxes. A closer look showed this to be correct. I was then told that I could turn in the mail in ballot if I wished to but they preferred I didn't as that would require them to call in to the county office to cancel my mail in ballot and issue me a new one. I was under the impression, having inquired several elections previously, that ballots were not tied to a particular person, so I asked if the ballot was marked in some way to identify it specifically and was shown a number along the edge which I was told was unique to that ballot and linked to my name. I then went to one of the carrels and filled out my ballot, signed and sealed the envelope, etc. Saved me a stamp at least.

Anyway TL;DR: In California, at least in Mendocino county, there is a link between you and your ballot.

This implies to me that it is possible they know exactly how you voted that ballot, i.e. ballots are not anonymous.

It also suggests that if they wished to they could tell you exactly how your ballot was counted so you could in theory do an audit of one. Imagine if every voter were to do that.