>>107713665
Nevermind, it is mode-line-frame-identification. Seems to be a terminal/msdos thing
;; MSDOS frames have window-system, but want the Fn identification.
(defun mode-line-frame-control ()
"Compute mode line construct for frame identification.
Value is used for `mode-line-frame-identification', which see."
(if (or (null window-system)
(eq window-system 'pc))
" %F "
" "))