| Clue | Source | Date |
|---|---|---|
| Signals for air traffic controllers | Newsday | 14 May 2019 |
| Spots for air traffic controllers | New York Times | 08 Jul 2016 |
| Spots for air traffic controllers | ||
| They're seen in control towers | Universal | 15 Nov 2015 |
| They're seen in control towers | ||
| They're seen in air traffic control towers | ||
| They're seen in air traffic control towers |