I've travelled places where a single note is worth very little, so I needed to carry enough that if they were USD could be perhaps $8K. Nobody seems to notice.

I've travelled places where a single note is worth very little, so I needed to carry enough that if they were USD could be perhaps $8K. Nobody seems to notice. Money launderers can expect to pay at least 10% of face value in "fees," perhaps up to 30%. So if someone wants to launder $100K they might be willing to pay $20K to get it done. Let's divide the money among ten mules, and one of those gets caught or defects, losing $10K. That leaves $10K total, $1K per mule, for "travel expenses." That's enough for each to book plane tickets and take a few hundred back home. For you and I, doing this would make no sense. For plenty of people in the world, it could be the best career opportunity they have. It's not really clear to me how we can expect to stop this, apart from some more obvious markers in bills to show up in airport (and seaport) scanners (imagine embedding the Audi logo using metal film in every note--something like that).