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Today’s high-resolution image scanners and colour printers are making it easier to create realistic forgeries of bank notes, cheques or share certificates. Now Swiss company Kbagiori has filed a patent application on a simple way to make fakes easier to spot (WO 03/099579). Instead of printing two unrelated serial numbers on each bank note, the second number is calculated from the first using a secret cipher. So unless would-be forgers obtain the cipher, they will not be able to work out what the second number should be, and any fakes will have pairs of numbers that don’t tally. For added security, the second number could be printed in an ink that can only be seen under UV light.