The scroll engraving is (IIRC) Photo Chemical Etching.
Kind of outdated now and used in it's place for such things would be Laser Photo Etching which is much more detailed and realistic to hand done art work.
But when these guns were made up, Photo Chemical Etching was about the best available,,and fast and cheap.
The pattern could be etched into the steel in a matter of a couple of minutes at the depth & quality they seemed to be happy with here.
The 'U.S. Springfield' lettering may be a roll die,,I'm, not sure.
The American Eagle symbol as well.
These two markings were done on all of the H&R Trapdoor's they produced.
The scroll engraving was done to some of the Trapdoors from H&R,,but not all.
Special run/Deluxe type stuff and then I believe there were a couple different patterns of engraving,,different editions or models,,what have you.
This scroll pattern is a rather crudely hand drawn copy of some of the orig engraving found on a few of the orig Trapdoor's especially made up as presentation pieces.
The originals vary in pattern.
The H&R Trapdoors have case colored locks but I don't know if they are actually 'hardened' or not. Some doing the process back then as well as even now are colors but little or no hardness.
About all I recall,,might be wrong on some of it. It's been a while.
FWIW,,Secure the locking lug in the breech of the recv'r on the H&R's. A simple set screw will do it, Search the net will get you all the info about it.
A few of these have a tendency to pop open sometimes when fired and auto eject the fired case past your noggin.
Easy fix, makes them a good shooter.