The system just uses a few markers, punctuation and sizing to denote things like on which beat a word comes in on, where the beginning of a measure is, what words to emphasize, where to pause, and which groups of words to give "triplet" rhythm to (where syllables are run together to fit into a smaller time constraint.
The biggest problem with some of my rap lyrics was that they would have pick up beats, and I might forget that and place the first word of a line on the first beat, which wouldn't sound late until halfway into the verse, when things would not link up right and I couldn't carry the verse through. So I started making a mark above the word that would come on the first beat. However, I don't mark every beat one in a verse, just the first beat one, because if I get that in the right spot, the rest falls into place. The system was developed, after all, mainly from first writing normal verses and then going back and marking them up.
Next I was forgetting when I had done triplet words, so I would space the (usually two) words together closely and underline them. Sometimes, also, I'll hold a word to fill out a beat or a beat and a half, and I'll put a line (sort of like in common practice lyric arrangement) to tell me to draw it out.
I noticed after that that I was indeed using normal punctuation, but sometimes in different ways than grammatically correct, to remind me of a) where pauses were, and b) where the ends of lines were (because that could be useful if I wanted to ever so slightly emphasize a rhymed word which often was at the end of a line - (careful though, over-emphasizing a rhyme makes a rapper sound cheesy ;) ). I used commas to denote pauses, and never in grammatical places, and semi colons to denote the ends of lines. Often I would use the semi colon method to save space, so a verse would be tightly packed on a page with no line breaks, and semi colons instead. When I typed them up, however, semi colons would turn into line breaks.
I also used size to denote emphasis, sort of like bolding or italicizing might be used, but in handwriting, there's no real bolding or italicizing, especially with my messy chicken scratch, so I was really left with size, especially since I was using underlining to show triplet rhythms. There are also cases where instead of enlarging a whole word, I simply capitalize the first letter, which tells me to emphasize it more subtly.
The system is good for rap tunes that I've already done outloud, because it reminds me what I've done. It's very quick that way. It would not, however, be that useful for communicating to a different rapper a fully realized "score", because of its relatively low amount of detail (for example, when a word is denoted as a pick up, is it an 8th note or a quarter note?). Then again, a given rap is only ever performed by its author (except in very rare cases of covering, like Rage Against The Machine's covering of various rap classics on "Renegades"), so this is not a concern for this system. Generally, having a system to communicate to myself allowed me to quickly create more complex and subtle rhythm schemes and not rehearse them much. Otherwise, I would've had to rehearse more before I could move on to new songs, and that would have slowed me down quite a bit.
Here you can see some examples. It was actually difficult to find or even
make up an example that uses all of the techniques. I also notice as I
scan examples how subtle the system really is.