If it’s the same as what was done here it is the record of whether you voted in a past election or not. The Democratic Party did that in Wisconsin in 2014. The mailer I received had something like 6 or 8 of my surrounding neighbors and me listing which of the previous 3 elections we voted in and which of the previous 3 elections we didn’t vote in.
I lean pretty reliably Democratic and was pissed off by this tactic. I know it’s a matter of public record but in my opinion it’s none of my neighbors business whether I vote or not.