Serial numbers of all old dollar bills are recorded when those bills are destroyed and replaced with newly printed bills AND when bills are deposited to banks. Even if fake bill is perfectly made, it will still be detected with this method. Fake and duplicate serial numbers will be detected when compared against official ones.

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echoangle 6 hours ago | parent [-]

Can’t you just immediately use them? The person getting caught will be some random person that took the bill, not the one bringing it into circulation.

	▲	httpz 5 hours ago \| parent [-]
		Trying to spend $1B with $100 bill at a time will take 10 million transactions. No one's going to accept large amount of cash without a credible source.