Variable: diary-entry-marker
diary-entry-marker is a customizable variable defined in
calendar.el.gz.
Value
diary
Documentation
How to mark dates that have diary entries.
The value can be either a single-character string (e.g. "+") or a face.
This variable was added, or its default value changed, in Emacs 23.1.
Probably introduced at or before Emacs version 19.24.
Source Code
;; Defined in /usr/src/emacs/lisp/calendar/calendar.el.gz
;; These briefly checked font-lock-mode, but that is broken, since it
;; is a buffer-local variable, and which buffer happens to be current
;; when this file is loaded shouldn't make a difference. One could
;; perhaps check global-font-lock-mode, or font-lock-global-modes; but
;; this feature doesn't use font-lock, so there's no real reason it
;; should respect those either. See bug#2199.
;; They also used to check display-color-p, but that is a problem if
;; loaded from --daemon. Since BW displays are rare now, this was
;; also taken out. The way to keep it would be to have nil mean do a
;; runtime check whenever this variable is used.
(defcustom diary-entry-marker 'diary
"How to mark dates that have diary entries.
The value can be either a single-character string (e.g. \"+\") or a face."
:type '(choice (string :tag "Single character string") face)
:group 'diary
:version "23.1")