Currently the rules are different in states that have adopted ANSI 117.1 and states that have not.
The original Code Of Federal Regulations is still the document of law in all states.
States that have not adopted ANSI 117.1 may have only the COFR to govern ADA Standards. The current COFR does not require upper case Braille letters. Tactile text must be all uppercase. Braille can be upper case, lower case or the first word Capitalized...it is up to you.
The guidelines you often hear people speak about have not been approved and therefore are not a legal requirement.
So, if you live in a state that has adopted ANSI 117.1 that is the document you must comply with along with the COFR.
If you live in a state that has not adopted ANSI 117.1 then the COFR is probably the only document in effect.
Note that the ANSI Standard is just that "A Standard".
State and local laws may be more restrictive than the Code of Federal Regulations but they must meet the minimum requirements of the COFR because it represents a Law passed by Congress.
A Code has precedence over a Specification or Standard.
Here is a link to 28 CFR Part 36 in PDf format...download this document if you fabricate ADA signs. Look at section 4.3 for information concerning signage.
http://www.ada.gov/adastd94.pdf
ANSI 117.1 requires Braille capital letters only be used before the first word of sentences, proper nouns and names, individual letters of the alphabet, initials or acronyms per section 703.5.4
.