Pics are a bit fuzzy when I blow them up, and can't read the markings on it. Does that have a mirror set in it at a 45 degree angle?
If so, in the M14 days, we had a "coach's scope". Snapped over the rear sight of an M14. You looked THROUGH a partially silvered mirror. Your coach, lying beside you looked into the angled mirror, allowing him to check your sight picture and sight alignment. Coach had the same view of sights as shooter.