You can make relevant anything in your writing that you want to make relevant: like writing commas inside shorthand texts in this case. In my years of writing, I've never written a comma in my own notes, ever. However, I can understand if you want to be precise for some reason or if you need to share text with someone. My general point is that if you need to write a comma for whatever reason, you don't need to make a new symbol for it, and that there is no need to reinvent the wheel: make it known that what you write is a comma and nothing else, whether is by circling it or by placing under the line, or whatever method you decide. You say having encircled commas is OK for teaching secretaries to place commas when typing their notes but not relevant to keep a record of your own notes. But the secretary types the notes to keep a record too, so in fact, you are doing exactly the same as the secretary is doing, but this time in your own shorthand text! Like I said, eventually it is you who needs to make sure that can read your own notes. I won't be mad if you don't follow my suggestion — it's your writing and I don't intend to see it. But saying that circling commas only applies for teaching secretaries where to place them, and not for distinguishing commas is like saying that a paper clip is only good for holding papers together. Lastly, I would think that if commas were an issue in shorthand writing and needed a special symbol, Dr. Gregg himself would have thought of something when devising his system.

Incidentally, Pitman Shorthand doesn't use commas either. Maybe the Pitman writers in the forum can share what they do.