indicate-unused-lines

indicate-unused-lines is a variable defined in `simple.el'.
Its value is

nil

• Automatically becomes buffer-local when set.
• This variable is an alias for `indicate-empty-lines'.

Documentation:
Visually indicate empty lines after the buffer end.
If non-nil, a bitmap is displayed in the left fringe of a window on
window-systems.

You can customize this variable.