Apart from "why would you want to?", I believe it's the blue ring. Not that you should have anything sewn onto your CS95's, strictly speaking. I think it's just for your No2/1 dress. Although if you don't pass next time you will have to take it off and you'll be left with the holes/discolouration.
I was a marksman for a number of years and I didn't have a badge sewn on any of my uniform.
Edited to add: I agree with; prove it on the range.