ABRSM is probably the main one used in the UK, and it's actually rather common worldwide, so it's a fair thing to state an ABRSM grade.
They go from 1-8 and then you can get a Diploma, Licentiate, and Fellowship of the Royal Schools of music.
I don't think I've met many FRSM holders.
I know a lot of people with DipABRSM, but it's still really hard to get.