I should point out that I've been using an accent of my own invention to indicate the difference between word forms. It's a little angle 'hat' accent on top of the letter (â, ê, î, ô). I'm suggesting a new accent because using a horizontal line for two different meanings seemed odd/ambiguous to me.
A summary of accents as I understand them:
The feminine is a horizontal line on the last syllable that, according to Gajewski, was intended to be put over the syllable (dō, rē, mī, fā, sōl, lā, sī) and was only written after the letter in his book because he abbreviated everything. It's pronounced by prolonging the vowel.
The plural is an accute ( ' ) accent above the final consonant (written by Gajewski after the letter (d'o, r'e, m'i, etc.)) and pronounced by prolonging the by prolonging the consonant as if there were two (ddo, rre, mmi...)
To indicate various parts of speech (noun, adjective, person doing something, etc.), a horizontal line is also used above the syllable. Gajewski also writes this after the abreviated letter, so it's difficult to tell if it was meant to go over the vowel, like the feminine, or after the consonant, like the plural. According to Sudre, this one is a stress accent, pronounced by putting a sudden emphasis on the syllable.
The reason I wanted to use another symbol is because it seems needlessly confusing to use the same symbol for both, when they represent completely different pronunciation and meanings. Also, when putting accents over shorthand or music notes, it seems best to have different symbols, since you can't tell if it's over the vowel or the consonant. I thought of using the little pointy accent thing because it resembles an accent that would be used in music.
Obviously I'm not going to instate a new standard without asking first, so... Thoughts?