Variable: comment-start
comment-start is a buffer-local variable defined in newcomment.el.gz.
Documentation
String to insert to start a new comment, or nil if no comment syntax.
Probably introduced at or before Emacs version 21.1.
Source Code
;; Defined in /usr/src/emacs/lisp/newcomment.el.gz
;;;###autoload
(defvar comment-start nil
"String to insert to start a new comment, or nil if no comment syntax.")