It's most notes, and for EU and US notes (as well as some others), it's based on a certain pattern on the bills: https://en.wikipedia.org/wiki/EURion_constellat

It's most notes, and for EU and US notes (as well as some others), it's based on a certain pattern on the bills: https://en.wikipedia.org/wiki/EURion_constellation https://en.wikipedia.org/wiki/EURion_constellation