I've noticed that some of the keys in the piano roll of the Midi Editor in Music Maker are labeled (c1,c2, c3, etc.). How do I get the rest of the keys to show note labels?

Somehow I got them to show up on accident one time, but don't know how I did it. Is there a keyboard shortcut or some combination of button click / mouse action that will show the notes in the piano roll?

Thanks for any help!