internal-lisp-face-p

internal-lisp-face-p is a built-in function in `C source code'.

(internal-lisp-face-p FACE &optional FRAME)

Return non-nil if FACE names a face.
FACE should be a symbol or string.
If optional second argument FRAME is non-nil, check for the
existence of a frame-local face with name FACE on that frame.
Otherwise check for the existence of a global face.