There's even an official per-mille symbol: ‰

My graduate advisor loved slipping it into papers just to show it off. I had to dissuade him at least once because it was in the middle of a table of percentages and who is going to that the 7th entry out of 12 has ‰ instead of %?

Blood-alcohol levels are typically measured as permilles in some countries, like Sweden. 0.2 ‰ is the legal limit there. Also used in some countries in Europe to denote the grade of slopes (as in warning for steep hills).

Never seen permyriads, though.