Just be careful though, They might be able to throw the book at you for defacing money. I wouldn't buy a stamp via traceable means like ebay. Also they could link defaced bills back to your individual stamp if you make your own. Just some things to consider.

I read some other comments to that OP, here are 3 of my favorites:

It's actually only worth 13.50

is that aunt jemima?

and

Cant wait for people to call these silverbacks

lmfao.

According to Title 18, Chapter 17 of the U.S. Code, which sets out crimes related to coins and currency, anyone who “alters, defaces, mutilates, impairs, diminishes, falsifies, scales, or lightens” coins can face fines or prison time. The same goes for debasing – that is, decreasing the proportion of precious metals – in gold or silver coins struck or coined at an American mint.

Similarly, anyone who “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,” can be fined or imprisoned as well.

It is.

https://www.livescience.com/34286-legal-or-illegal-to-destroy-coins-paper-money.html#:~:text=According%20to%20Title%2018%2C%20Chapter%2017%20of%20the,lightens%E2%80%9D%20coins%20can%20face%20fines%20or%20prison%20time.

I wouldn't recommend doing it repeatedly at the same place. Spread em around.