Edit: oh heck. It might have been The Diamond Age.
Edit 2: search yielded
“Bud knew a guy like that who’d somehow gotten infected with a meme that ran advertisements for roach motels, in Hindi, superimposed on the bottom right-hand corner of his visual field, twenty-four hours a day, until the guy whacked himself.” --Neal Stephenson, The Diamond Age
I was trying to find information about this restriction. It seems it applies to cash and relates to Danish banks’ ability to implement AML controls. https://www.nationalbanken.dk/en/what-we-do/notes-and-coins/exchange-of-danish-cash-abroad