Grading

 A Scrum Master is accountable for the effective implementation of Scrum, while agile coaching is one of the stances a Scrum Master may adopt at certain times. Does that sound like the sort of thing that even can be graded?

Organizations love their hierarchies, even to the point that they may try and superimpose their very change agents onto these structures. As such, the "gradings" you describe may represent an impediment to agile practice which ought to be challenged and removed.

Organizations love their hierarchies, even to the point that they may try and superimpose their very change agents onto these structures.

This point resonates with me so much. The grading system most of the time imposes certain things on the Scrum master/Agile coach which may not be something they are supposed to do. One common method might be 360 degree feedback to check with the team on the benefits they have had having a scrum master. Points like how has he/she facilitated continuous learning so on and so forth.

In fact I have another question to ask "How do Scrum masters showcase what they have achieved?"..would like to hear from experts on this question as well.

What is the purpose of grading ? It all depends on the roles and responsibilities of the position you have in your organisation and it defers to company to company. There is no defined border to such grading for Scrum Master or Agile Coaches and that can not be defined just based on the experience for sure.