R.N. Elliott developed his own labeling system to accompany his discovery of the wave principle back in the 1930’s. His labeling system consisted of both upper and lower case case letters, as well as Arabic and Roman numerals. Some labels were to be circled, and others were placed within parentheses. Some labels were without either circles or parentheses. As you can imagine, this type of labeling system is quite cumbersome to reproduce inside most charting platforms today, so the following is the color coding system (and associated font size) that I use to label the waves.
For reference, here’s a table of Mr. Elliott’s original labeling system: