Well but see the intent isn't to render it unfit to be reissued, the whole point is that you want it to stay in circulation so as many people as possible see the additional message.

The MAGoos have been stamping 'Donald Trump Lives Here' on US currency for years.

They are supposed to do it on bills that show the White House, but they've also put in on $5 bills that show the Lincoln Memorial

To be fair, there's a whole lot of difference between defacing a banknote vs. rendering it unfit for issue.

In any case, cause of how often it changes hands, and how little supervision its under, it'd be very difficult to actually identify who defaced a specific note - especially if you've git a whole bunch of people doing it to a whole bunch of notes

As someone else already pointed out, the "with intent to render such [...] unfit to be reissued" part is key here.

The Stamp Stampede has a good resource on this.

Essentially, the argument just boils down to the fact that you're... not making the bill unusable. As long as the denomination is still visible and not altered to another number, and it's possible to see anti-fraud measures like the green seal well enough, you're not rendering it unfit for circulation.

There is the problem of ATMs sometimes rejecting stamped bills (or accepting them but having the bank send them back to the Fed to be replaced with new, clean ones) but afaik it's rare and not too likely as long as you don't cover the denomination.

Most businesses don't reject stamped bills as they have no reason to expect additional markings would mean a bill is actually NOT real, and most people won't decide to just never spend it again because it has a stamp.

As long as you don't promote/advertise a business, or change the actual denomination of the bill, you're fine.

They would first have to prove that you were the one who did it. Good luck with that.

with intent to render such […] unfit to be reissued

This isn't trying to take it out of circulation tho, so that probably wouldn't apply. They'd have to make an argument that effectively goes against the first amendment to say you can't write on currency you plan to spend.

“rendering unfit” is when you glue $20 corners to a $10 to pass it off as a 20.

On the other hand, freedom of opinion might save your butt.

It almost certainly would... if you have the money to win a lawsuit on First Amendment grounds, which is far from cheap.

there so much defaced money already out there

you'd have to really make a big scene where it makes a lot of noise to even stand out

Arguably relevant precedent:

https://supreme.justia.com/cases/federal/us/430/705/

Nah, totally legal. As long as you make sure you don't draw over anything renders it unfit for reissue

It would be almost impossible to pin it on anyone.