The clear areas are in relief, raised from the surroundings. I'm familiar with etched molds (they're common in Depression glass), but to me this doesn't seem like etching (alone at least) of either the glass or the mold. With etching I'd expect to see "flat" areas of different depths corresponding with the amount of time the mold/glass was in the acid. The topography doesn't look right to me for that, but maybe there's a process I don't know about. The OP describes it like canyon walls in miniature. And the edges of the blank areas are quite sharp, another thing I wouldn't expect with an etched mold. Wouldn't it have to have been pressed to get detail like this to show? Yet there are no mold marks, and you'd think in the process of eliminating them you'd end up getting rid of sharpness in the design.
With sandblasting, on the other hand, you might be able to aim the stream enough to give it more of a carved look. That could be followed by etching to polish it.
As for the mark, I don't get the FBS thing. All I see is a 5 (possibly an S). Am I missing something?
And Verame - a poster who claimed he knew whereof he spoke said Verame was a mystery, and no one even knew for sure whether the company was Czech or French. Is it a mystery? Is Verame = Verrerie d'Art Lorrain?