UI indication that a window is currently in fullscreen mode

[samuela]

Having the ability to temporarily break the layout and make a single window fullscreen is useful. However, looking at a fullscreen window, there is no indication AFAICT that I am looking at a window in fullscreen mode as opposed to a workspace with only a single window.

Is there a way to give the user some indication that they are in fullscreen mode? Perhaps something like service mode where the menu bar goes from 1 to [s] 1?

[Hylian]

Being able to query fullscreen status via something like aerospace list-windows or aerospace list-windows --focused --fullscreen would be handy for displaying the status in Sketchybar.