Also, this little "o" placed after a capital N means "number" in French (No
1, No2, etc.) but in modern typography there shouldn't be any small line
below it, or below any "suscrit" character. The use of drawing a small line
is more typical of handwriting. Anyway, the proofreading indication for a
suscrit character is a couple of small lines (vertical or oblique) below the
typed or printed character.
I don't know what the little "o" with a line below it means. I realize I
haven't answered your question at all. Sorry!