First, let's start with how do you insert Hidden Text? Well, press Alt+I+H and the Hidden Text dialogue box opens up. Now, you can type whatever you want into the box. This is great for communicating with your scopist or yourself to remind you to get a spelling or to check something.
You can insert exhibit index format symbols to mark items like questions instructed not to answer, questions marked for a ruling, and lines for information requested.
You can create a macro or an Accelewriter to open a Hidden Text dialogue box to insert notes and then close the box.
By the way, what you'll see is a green push pin in your transcript while in edit but you won't see it in the transcript.
Just like the OOPS format symbol you can also print a list of all your hidden text out or open up the Hidden Text dialogue pane for reference.
Go ahead, try it out and enjoy.