Thank you for such an interesting question.
There are no clear cut rules that address this particular situation.
This is one of those times that a transcriber would have to study the situation carefully and make a judgement call.
I have conferenced with a number of people about this issue. I've been given two very different answers.
Yes use the letter sign.
Since we have no clear rules about to handle a situation like this, follow the rule that says the slash does not terminate a number.
No do not use the letter sign.
The only specific rule we have about using the letter sign after the slash refers specifically to letters.
Both opinions are equally valid.
Please remember that these are merely opinions and do not reflect a right or wrong way of handling this situation.
If you are brailling this for an agency or for a specific student, I would ask the agency's or teacher's preference.
Otherwise, use your transcriber's discretion and stay consistent with whatever you chose to do.
Sorry I could not give you a more specific answer.
Thank you for your patience,