That is what I would love to find out, maybe it is just the export mark of one particular wholeseller, maybe it is even another company that produced in Martinuzzi's style. There are also pieces that are very reminiscent of Martinuzzi's designs, which are just marked in two lines MADE IN ITALY, no frame around the words...
Was the mark for Zecchin-Martinuzzi or just for Martinuzzi?
The Zecchin form Zecchin Martinuzzi Vetri Artistici et Mosaici is often mistaken to be Vittorio Zecchin who worked like Martinuzzi for Venini in the early twenties and designed glass just like him. This Zecchin is Francesco and was an engineer as far as I remember who was likely rather in charge of the technical and financial issues than the artistic ones...Other designers did thus work for Zecchin-Martinuzzi...
Also Alfredo Barbini was working in this company before setting up his own, were Martinuzzi continued to design sculptural glass until the seventies and I am sure there were many more stations for Napoleone Martinuzzi during the years inbetween.
So if anybody has an idea about that particular diamond style export stamp...Which company could it be, is it by a company at all? What age do those art deco style pieces marked that way really have?..