Vintage/Antique Steel Bird Dog Bookends with "O.S." stamped on one tail and "R D Applied For" on other tail...

I have a pair of Vintage/Antique Steel (hollow) Bird Dog Bookends with "O.S." stamped on one tail and "R D Applied For" on other tail. Each bookend measures about 6-1/2" long, weigh approximately 4lbs each and, as you can see, are highly detailed. The dogs are mounted onto the bookend bases with machine screws. They appear to have been sand blasted/prepped for painting. I have not had any luck whatsoever finding information on them - any ideas/opinions would be greatly appreciated.

Thank you!