Curious about the initials D.R.G.M. ??? Ya see 'em on German whistles sometimes.
Registrations are different than patents. Some interesting reading about it at the following link…
I like the part about poor mans patent !!!! Just received a cheaply constructed whistle from Germany with that stamp and thought you might want to take note of it ( saved here anyway ) —- you know, for your records…. helps in dating them too.
Hmph…cheap whistle construction….at least it has a stophole 🙂