global-auto-revert-mode-text

global-auto-revert-mode-text is a variable defined in `autorevert.el'.
Its value is

""

Documentation:
String to display when Global Auto-Revert Mode is active.

The default is nothing since when this mode is active this text doesn't
vary over time, or between buffers. Hence mode line text
would only waste precious space.

You can customize this variable.