Related Clues:
- Informal letter public school circulated
- Handwritten surprise in a lunchbox
- Musical sound, and an anagram of 29-Across
- Obsolescent document transmitter
- B sharp or B flat
- Musical scale part
- La or ti, e.g
- Record contribution to score
- Something passed after saying "Psst!"
- Number on older business cards
- A, perhaps, with or without IOU?
- Make a mental ___
- Communication that may baffle millennials
- Phone-y document?
- One might be passed in class