You're right that most Lobmeyr was signed after 1870, but not all of it, and if it was signed in gilt it could have worn off. However this doesn't really look like Lobmeyr to me.
Marcus, have you seen Lobmeyr in this style? I agree that Haida is a possibility, but the gold I would think makes it less likely, no?
Nancy, how did you come to think it might be Prutscher?
I find this kind of cut-to-clear work hard to pin down. It was done in America, France and England as well as in Bohemia, where it continues to be made. I'm sure there's variation by date and region, but there was also overlap. The gold is a clue; can you tell if there was any design to it, or was it just gold lines bordering the windows?
It looks like the surface it a bit mottled, kind of like it was acid polished. Is that true? Is it inside or outside?