A stroke of unicity
A banknote was printed on a large sheet. The first layer consisted of blue ink. The rest then followed: seals, hand-written serial numbers, and date.
Some elements were copied directly next to the print. That was how a receipt was made. In that way, circulating banknotes could always be checked when laid next to this left-behind piece of paper. Stamps that partly landed on the paper money and partly on the receipt made this check almost waterproof.
But there was a final trick to gain the thrust of the people. To show how serious the check was, a certified official would loosely add a brush stroke.
Such a brush stroke would, just like some stamps, cover both the banknote and the receipt. This brush stroke could be considered a fingerprint, even more so than the hallmarks. Uncopiable! Now truly everything was done to gain the trust of the people. No forger dared to even try.