Found what I was looking for. According to Fricke (1983):
Fin ray type
A: Spines. Symbol is Roman numeral upper, example I, II, III, IV, V, etc.
B: Segmented branched soft rays. Symbol is Arabic numerals (Fricke called them Indian numerals), example 1, 2, 3, etc.
C: Segmented unbranched soft rays. Symbol is lower case Roman numerals, example i, ii, iii, iv, v, etc.
0: Unsegmented unbranched soft rays. Symbol is lower case Roman numerals in parentheses, example (i), (iv), (v) etc.
Paper: Ronald Fricke, "A method of counting caudal fin rays of actinopterygian fishes," Braunschweiger Naturkundliche Schriften 1 (4), 1983, pp. 729-733.