Wolf of Wall Street: they needed to physically move cash to Switzerland so they literally tied hundred dollar bills to a Swiss-American girl's body and had her take planes to Switzerland. Main character is eventually busted because one of his partners is caught transporting this cash to the Swiss girl's boyfriend. Partner then turns on him.
Well, there is a possibility that the guy they hired to inspect packages or something, identified the QR paper wallet address as a Bitcoin address.
The ultimate way to do this would be to memorize a brainwallet, then there's no way in hell they would know, because the money is literally in your brain
An encrypted private key could be embedded in a picture of your dog that's floating around on imgur or photobucket. There is no limit to the number of ways it can be taken across borders.