Banknotes for all leading currencies worldwide contain magnetic safety signs, that are used for detecting counterfit banknotes. 

Using basic or handheld devices to detect counterfit notes using the magnetic properties of the ink is one of the least reliable of detecting forgeries, as using readily available magnetic ink printers can easily bypass those detectors.

On the other hand using more advanced devices it's more reliable as those devices such as `cmos-magview` can detect not only the precence of a magnetic field, but also it's strength.

You can find more information about the magnetic inks used in banknotes in this links:

[1]: https://matesy.de/en/products/magnetic-field-visualization/applications/investigation-and-quality-control-of-bank-note-safety-features

[2]: https://www.etesters.com/product/D99F53E1-6711-460F-9219-49E55BA17268/cmos-magview-magnetic-field-viewer-and-measurement-device/

[3]: https://blog.fraudfighter.com/bid/54746/Detecting-Counterfeit-Money-Magnetic-Ink-Watermark-Lamps
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