International copyright secured???

[Starrmark]

Every now-and-then, I come across the phrase 'International copyright secured' printed on published musical scores -- including some scores that were published by major American music publishers as late as the 1960s. What does this mean? Wasn't/isn't a plain vanilla US copyright also an International Copyright?

If a work was copyrighted in the US in the 1960s or later, wasn't that US copyright valid in all countries that signed the copyright treaty? Is an 'international copyright' something on top of a US copyright? Why was it necessary to secure an 'international copyright' -- and is it still necessary to secure an 'international copyright'? Who issues 'International' Copyrights?

Now, of course, musical works are protected by copyright the moment they are fixed on paper (or in digital form), even if they are not registered with the US Copyright Office. Is a non-registered US Copyright also an 'International copyright'? Does one have to include 'International Copyright Secured' on the front page of scores copyrighted in the US in order to protect a score outside the US?

MS

[vinteuil]

It doesn't really matter for our purposes, because when copyright laws change in the EU and CA, the changes are retroactive. Thus, since their is no current need to secure international copyright for U.S. publications, this phrase is completely meaningless. "All Rights Reserved" etc. is also pretty meaningless, although if I remember, that guarantees the possibility of some sort of restitution...