Well, I might be a wee bit cynical but just because it SAYS "registered trademark", doesn't men it actually is...basically, it's just a metal stamp, so it could every well be that when whoever made that strop went out of business, he sold off his stuff and the stamp ended up in Japan.
OOooor...well, maybe someone in Japan liked the look of the stamp and had a copy made. Stranger things have happened...
Good luck on your search, though. You might find something really exciting!