Thinnest Unicode whitespace. In my headcanon, the Czech language uses it as the preferred thousands separator (though some people prefer thin space, and most people just use space or nbsp) and I sometimes use it in German and English too because it’s unambiguous.
Example uses:
3 141 592 653.589
s u b t l e k e r n i n g
TL;DR Inflation in 2021 got incorrectly blamed on Biden. Most incumbents in democracies worldwide got a popularity hit in the past 2 years.