Tmux: no pane 'zoom' indication after customising status bar

From tmux 2.0 onward, you can use the #{?window_zoomed_flag,ZOOMTEXT,NON-ZOOM TEXT} replacement conditional in your window-status-current-format string.

For example, I use:

#{?window_zoomed_flag,#[fg=red](,}#W#{?window_zoomed_flag,#[fg=red]),}

To surround the window name with red parenthesis when it is zoomed.

You want to use the window flags option in your customization, which is #F.

Note that this is the same flag for indicating that a window is active, etc. I don't know of a way to show the zoom indicator but not show the other general window status indicators.

You can check out the Formats section in the tmux man page for the full list of options.