Use the following in your ~/.emacs file have Emacs display a little marker in the left fringe for window area not part of the buffer (ie. not filled with empty lines):
(setq default-indicate-empty-lines t)
Or temporarily use M-x set-variable to set ‘indicate-empty-lines’ to t.
For Emacs 20:
From: Samuel Padgett Subject: Re: Highlight end of buffer Newsgroups: gnu.emacs.help Date: Tue, 16 Oct 2001 19:48:38 GMT
(defun my-mark-eob ()
(let ((existing-overlays (overlays-in (point-max) (point-max)))
(eob-mark (make-overlay (point-max) (point-max) nil t t))
(eob-text "~~~"))
;; Delete any previous EOB markers. Necessary so that they don't
;; accumulate on calls to revert-buffer.
(dolist (next-overlay existing-overlays)
(if (overlay-get next-overlay 'eob-overlay)
(delete-overlay next-overlay)))
;; Add a new EOB marker.
(put-text-property 0 (length eob-text)
'face '(foreground-color . "slate gray") eob-text)
(overlay-put eob-mark 'eob-overlay t)
(overlay-put eob-mark 'after-string eob-text)))
(add-hook 'find-file-hooks 'my-mark-eob)