Super regional, remember learning 15$ in French class but using $15 everywhere else because I’m an anglophone. Personally, as someone else said, it’s a unit, totally makes sense treating it as such and I do tend to use iso currency codes when talking dollars because I’m Canadian, 40 USD is 54.75 CAD, 40 CAD is 29.23 USD, if I don’t specify that it makes things look way more expensive comparatively.