Sauce on the watermark?

Ballots are secure, knowledge on vote-by-mail is not

Contrary to suggestions that mail-in ballots can be easily reproduced and counterfeited, the physical characteristics and printing methods of the ballot and envelope would make that task extremely difficult. Each state or locality sets its voting rules and the means of voting, including the ballot format. Ballots, like money, are printed on special fraud-resistant paper, with particular size, thickness, weight, texture, color, and formats made to exact specifications. Furthermore, the paper is impressed with unique identifiers, such as watermarks, that certify it as an official ballot. Ballot envelopes contain many of the same anti-fraud protections, with some jurisdictions including unique bar codes on the envelopes to help efficiently process ballots.

https://www.law.upenn.edu/live/news/10346-ballots-are-secure-knowledge-on-vote-by-mail-is