Variable: compilation--margin-string
compilation--margin-string is a variable defined in compile.el.gz.
Value
#("=>" 0 2 (face default))
Documentation
The string which will appear in the margin in compilation mode.
Source Code
;; Defined in /usr/src/emacs/lisp/progmodes/compile.el.gz
(defconst compilation--margin-string (propertize "=>" 'face 'default)
"The string which will appear in the margin in compilation mode.")