Note that this isn't normal copyright, the red cross is protected under the Geneva Conventions
https://en.wikipedia.org/wiki/Emblems_of_the_International_R...
A green cross would confuse people.
Where do you get this confidence that there's no confusion with the green cross?
The continents of Europe, Africa, Australia... I've also seen it used in China but I'm not as familiar with Asia because I haven't lived there.
I'm sorry, but if your only example is the US then you're likely to be wrong about a lot of things.
That is uncalled for.