I vaguely recall this happening as a joke in some form of media but all I’m getting are statistics about currency being contaminated with cocaine when searching for it online.
Edit: My dad wants to buy scuba equipment but doesn’t know where to buy it or what size he is for a lot of it so I was going to write “For scuba equipment not for drugs” on one of the bills as a joke for his Christmas present.
Could be related to the Aussie movie Two Hands, where some drug money has a picture of a gun drawn on it? Only one I can think of right now where money has somat written on it.
That and the tooth fairy sticker on the fiver in that Bluey episode, I guess.