I have an entire silver service with this exact marking. I also have a plate. It was passsed down to me from my grandparents who lived and worked in Bogota Columbia during the Depression. I don't know what these markings mean, but with your items it is clear we are not alone. I have an aunt and uncle who possess goblets likely made by this same mine!!
I have four hammered silver wine goblets, I guess you would call them with the same atn mark as yours, but my mark looks more like the one posted on this page by rover. My Great Uncle brought them back from Columbia South America around 1920, he was an Engineer on a rail road project down there somewhere. If you find out anything else about the hallmark please advise, have been to several antique dealers and found out nothing.