Dave, I am not sure. Baker seemed to confuse these markings sometimes, too. P K E /NN is surely Paragon Krupp Ejector Nineteen Nine. I have seen P D, P K, N E S, L E S. And I am sure others. The first letter seems to be the Grade, Sometimes the next letter is Ejector, sometimes barrel material type, sometimes indicating a single trigger. Really, no hard and fast rules as I see it.
The F E S , in addition to the others is new to me. I can only guess that F might be Fluid, E might be ejector, S might be Steel or maybe the gun had a single trigger at one time. Oddly there are two S on the barrel lump and the font appears to be the same as in F E S. I have never seen this, either. For all we know F E S could be a man's name.