"Thank you for your question!
We know that our rulebooks cannot contain conclusive advice for every possible need, and your question highlights a case where we have to consider what the rulebooks do provide, and what the braille reader needs.
Not using a second symbol (e.g., the grade 1 indicator, a period, a capitals indicator) in the braille on the tactile in question will make it difficult to distinguish some symbols. For example, a "b" and "c" will be indistinguishable from one another, as will be a "d", "f", "h", or "j". For this reason we will refer to the following rules in GSTG, and GTM:
GSTG 188.8.131.52 One of the letters in each key entry must include dot 3 and/or dot 6 in the braille configuration....
GSTG 184.108.40.206 Single-letter keys are not recommended, but if used they must be followed by a period. Do not use the letter indicator before a two-cell alphabetic key, even when the letter combination corresponds to a braille short-form word.
GTM 4.4.2 ... This section does not attempt to give advice on how to effectively label a diagram in braille so that it is clear to the reader which part of the diagram each label refers to. Rather, it lists code accommodations which can be made within the content of certain labels when space is at a premium.
... When labelling points, lines etc. with single letters, these can be consistently shown as two cells by omitting the grade 1 indicator for all capital letters and including it for all lowercase letters including a, i and o.
All of the above rules specify methods for providing the braille reader with not only the single-symbol, but also an additional symbol for indicating the proper orientation when reading the letter symbol. This additional symbol is necessary to ensure the braille can be read accurately.
Based on the above, this committee's guidance is to follow GSTG 220.127.116.11 “Any combination of letters or letters and braille contractions requiring a minimum of two braille cells but not more than three braille cells may be used.” We suggest including grade 1 indicators for lowercase letters, and only the capitals indicator when capitals are to be used. This ensures the braille will include an orienting feature for the reader (e.g., the grade 1 indicator or the capitals indicator) so there is no risk of confusing symbols.
We also agree with you that a transcriber's note should accompany the tactiles so the braille reader knows how to interpret the tactiles properly."
On behalf of the Tactile Graphics Committee
Cindy Olmstead, Chair