You can put a personal note on any card in these stacks. A note is a pop-up field where you can enter some text. The note button hides or shows the note, once you've created it. You can only have one note per card.
To attach a note, simply press the Enter key. When the field appears, type in your note. Click on the asterisk to make the note disappear and reappear.
To delete the note, press the Enter key on any card where a note already exists.