small red glass domed light/lantern lens cover

I do not *know* what this cute little red lens was intended for, though I'd *suspect* it could have served duty on the outside of a commuter train car or something similar -- mostly because of where I got it, but also because it has residual dirt around the edge rim and some surface scratches/abrasion as if it was exposed to such an environment. I'm inclined to think against "automotive" both because it isn't branded as such and because I don't really recall any old car models that have used anything so non-stylized as its simple round domed shape, and I also can't think of any other kind of light or lantern I've ever seen that would have used something like it.

It is 3-3/4" across and 1-1/2" deep, with a fine crosshatch pattern molded into its inner surface, the outside is smooth with three small ridges/rings around its edge lip which also has a pair of notches molded in to keep it stationary in whatever kind of light fixture. Pic 3 here shows it with a small flashlight underneath to give an idea of what it'd look like illuminated. There are no markings whatsoever.

Does anybody else have a better guess what it might have been for??