New key

This chrismas I received a key! Along with a vintage power supply and Morse sounder. It looks old and has some loverly green corrosion on most the brass bits. It sits atop a wooden base and that atop a steel slab with a rubber sheet glued beneath. It has PMG stamped on the front of the wooden block. Should scrub up well. Would like to find out more about when and where they were used. Will post pictures soon.