The port markers do not display if you have the Graphics settings, "Show Mining Drill arrows when detailed info is on" turned off. The port marker display should probably not be tied to any vanilla options.
I saw a video of someone using the port markers, but they wouldn't work in my own game. It took quite a while for it to occur to me that it might be tied to one of the arrow display options.
The port markers do not display if you have the Graphics settings, "Show Mining Drill arrows when detailed info is on" turned off. The port marker display should probably not be tied to any vanilla options.
I saw a video of someone using the port markers, but they wouldn't work in my own game. It took quite a while for it to occur to me that it might be tied to one of the arrow display options.