I just looked at my Micromega under a microscope. The reticle is on the outside surface of the lens. (You could put a fingerprint on the silver painted double rectangle if you touched it).
Also, by design I believe the visual projection of the reflection of the reticle should appear to be at the same plane as the paper surface, if you look down at the mirror with both eyes, so your left eye sees the reticle and the right eye sees the baseboard... I drew a rectangle on paper same size and placed it underneath so my eyes believed they were seeing one rectangle. The visual appearance was as if they are on the same plane. Parallax would show if they are out of place. Moving my head, the rectangles seem to stay visually in place. I suspect if the reticle was upside down (inside out), you might visually notice they are not in the same plane, and parallax would make the images move relative to each other when you move your head.