Mark yours is the second key like that I’ve seen since I found mine 10 years ago. W. H. Bracy filed patent number 189,600 on April 17, 1877 for it. I have researched him but can’t lay my hands on it right now.
Need a little help on identifying this for a friend. Belonged to a family member and now his. The markings on the movement have me a bit confused. I know little of Walthams.
Movement says from top to bottom on left side of movement.