Most of the world implemented the Berne Convention, which creates a thing called "copyright". In the world of copyright, absence of license means all rights reserved, except for "fair use", "fair dealing" and similar exceptions. In the world outside copyright law everything is in the public domain, no licenses necessary.
Well, you can have copyright without declaring that everything is copyrighted when it is created. A lot of countries had systems like that until they ratified the Berne Convention.
No, it wasn't implied, it was stated outright that the Berne Convention "creates a thing called copyright" (when, in fact, the Berne Convention harmonizes certain provisions of copyright law among those countries who adhere to it.)
Before 1989 the United States required a copyright symbol and year of publishing on every work. After 1989, i don't know of any country that still does this.
While I'm sure there is a legal system somewhere in the world that does that most places have automatic rights for intellectual property, even if you give it away for free. Trying to use this font for business would result in compliance issues, because it's unclear what you can and can't do with it.
https://en.wikipedia.org/wiki/Berne_Convention