Green Square on F6/F6F6 charts: Point of interest.
Player-marked system for reason chosen by player.
Setting Cody's Square
Go to F6F6 then Find Planet/enter planet name - that will put the green square on it, then select a different target system with mouse or cursor keys, and the green square will remain where it was.
Unsetting Cody's Square
Enter another planet's name (or even just one letter), then re-select your target system.
The dastardly villain Cody the Curmudgeonly bamboozled his software engineers to introduce a blood-red square onto the F6 Long Range Chart for his route planning... this was eventually turned green by the Long Range Chart specialist division of Williams Avionics who renamed it as the Rhomboid Route-Marker VG337a for the Astrogation console of the new Cobra Mk III.