| Clue | Source | Date |
|---|---|---|
| Whiteboard warning to custodians | Wall Street Journal | 26 Feb 2025 |
| Directive for the board | New York Times | 18 Feb 2023 |
| Chalkboard entreaty left for custodial staff | The New Yorker | 08 Jul 2019 |
| Chalked warning left for custodial staff | New York Times | 30 May 2015 |
| Chalked warning left for custodial staff | ||
| Admonition to a hit man? |