D.R.G.M. is some kind of patent insignia followed by the registration number 459. it's something like Deutsche Reich Geshmakmuster 459
the D.R.P. is deutsche reichspatent, or something similar.
it's a general "made in germany" like stamp, german patent?
the drgm is the more specific patent and registration that protected the item and inventor. at least that's how i understand it.
soryy about the spelling. when i was stationed in germany the locals wouldn't even let me try and speak the language because o butchered it so badly!
but, hey, welcome to the forum!
tom