minibuffer-depth-indicate-mode

minibuffer-depth-indicate-mode is a variable defined in `mb-depth.el'.
Its value is

nil

Documentation:
Non-nil if Minibuffer-Depth-Indicate mode is enabled.
See the command `minibuffer-depth-indicate-mode' for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `minibuffer-depth-indicate-mode'.

You can customize this variable.