Hi Carl,
I have that symbol on a few old lamps made by Ediswan and Osram for military applications. I am not quite sure what it means, but Admiralty lamps often tend to bear this symbol, and other similar symbols are marked on special proprietary lamps for the Air force and other military groups. So my opinion is that it is referring to the user of the lamp, rather than its manufacturer.
Tim - Siemens' early symbol is very similar, taking the form of an "S" with a small letter "H" superimposed over its centre at 45 degrees. The S and H stood for Siemens & Halske, the name by which the company was known shortly before its merger with AEG to form Osram.
James