Let us dispel some rumor here. These were not converted to a "Trench knife" or any sort of military function. They were sold out of service, and this example even bears the proof. It shows the opposed broad arrows to prove it's disposal. They weren't taken "Back into service" after. These were ALL as far as I know done by Pal Tool and Knife to furnish civilian hunting knives as the rifle had mostly fallen from favor and saw little service after it's withdrawal. They were done and I've never seen a marking, this is why the story morphs into them being "Trench knives" of sorts. True, there were always soldiers looking to make a knife of some sort, some would invariably have been grabbed and bucked down. A very small percentage. I doubt you'll see a PAL marking. You usually don't even find the scabbards.
Here's a bit from others to confirm what I say.
Ross bayonet modified to be a Bowie-style knife - Requesting help identifying markings | Gunboards Forums