Even in the early nineties there were fears that new sophisticated readily available photocopiers/computer scanners & printers could produce pretty good forgeries if the right paper was used.
The thing is, US currency is all over the world, and is readily/instantly tradeable.
Its not a secure currency, its THE secure currency.
From $1 for a bag of avocadoes in Honduras, to $3000 for a high-tech gadget in Oman or Japan or wherever.
If you travel to a lot of different places, you eventually get fed up with the local crap and just carry a wedge of greenbacks.
Even in places like Japan and Australia, out would come the calculator, poke poke poke, that'll do nicely sir.
Recalling this cash would also open up the possibility of people trading cash USD (at a discount) for cash Euros, especially in third world countries and places where the authorities need to be avoided.
So cash euros might gain a significant foothold.
If the Federal Reserve recalled all this floating cash wealth around the world it would be a nightmare, especially for those who didn't want the authorities to know about their USD nestegg.
Was Saddam caught with a bag of Dinars from a middle eastern country?
Don't think so. The local toilet paper is for the peasants.
Osama and Kim Jong-il will also have holdalls filled with wedges of Uncle Sams finest filthy lucre.