Cruising the MCN website, looking at all the eye-candy. Came upon this. About the sixth picture down is the maker's mark on the ricasso of the blade. The guy swinging the hammer looked familiar. I have a M1889 Prussian officers sword with the same hammer guy, but the dagger shown here is marked "E. P. & S." and my sword is marked "P. O. & Co.". So digging a bit deeper, this is what I found. "E. P. & S." is "Ernst Pack & Sohns" and they produced edged weapons in WW2. Prior to that, Ernst worked with another guy named Ohliger, "P. O. & Co." is "Pack, Ohliger & Co." and they produced edged weapons from 1905 to 1925.
It seems (if this data is correct) that you would find "P. O. & Co." on pre-WW2 blades, and during WW2 you would see "E.P. & S."