Defacement of U.S. currency is regulated by 18 USC 333, which states:
[W]hoever mutilates, cuts, defaces, disfigures, or perforates, or unites or cements together, or does any other thing to any bank bill, draft, note, or other evidence of debt issued by any national banking association, or Federal Reserve bank, or the Federal Reserve System, with intent to render such bank bill, draft, note, or other evidence of debt unfit to be reissued, shall be fined under this title or imprisoned not more than six months, or both. [Emphasis added]
There’s also a law prohibiting the use of paper money as advertising, 18 USC 475, which states:
[W]hoever . . . writes, prints, or otherwise impresses upon . . . any [coin or currency] of the United States, any business or professional card, notice, or advertisement, or any notice or advertisement whatever, shall be fined under this title. [Emphasis added]
I would change it up slightly since it is illegal to advertise on the bills. But you can put political messages on them.
https://www.stampstampede.org/faq/yes-its-legal/
Defacement of U.S. currency is regulated by 18 USC 333, which states:
[W]hoever mutilates, cuts, defaces, disfigures, or perforates, or unites or cements together, or does any other thing to any bank bill, draft, note, or other evidence of debt issued by any national banking association, or Federal Reserve bank, or the Federal Reserve System, with intent to render such bank bill, draft, note, or other evidence of debt unfit to be reissued, shall be fined under this title or imprisoned not more than six months, or both. [Emphasis added]
There’s also a law prohibiting the use of paper money as advertising, 18 USC 475, which states:
[W]hoever . . . writes, prints, or otherwise impresses upon . . . any [coin or currency] of the United States, any business or professional card, notice, or advertisement, or any notice or advertisement whatever, shall be fined under this title. [Emphasis added]
The Federal Government nullified itself on January 6
It's not advertising because there's nothing being sold?