It has its roots in Latin. Mil means one thousand, so mil mil, aka million, is one thousand thousands. You'll see it in places that do more romance language family business, or in accounting where it's an old convention even in English.
Old-school banking, M is thousand, MM is million.
Sometimes MM is thousands monthly.
It a strange world.
Example?
I've seen it in person a lot in internal corporate presentations. Maybe they've all been wrong, but that's how language works.
M is also used for thousand in adtech - cpm is a cost per millie or cost per thousand.
movie production cards. roman numerals.
i would not expect that to be the case in this context. you would also probably never mix roman numerals and arabic numerals like that.