In the real world it's a Japanese naming convention, mostly for no-military ships (especially fishing boats) although that wasn't always the case. In literal terms it means "circle" and there are a few theories as to it's significance, but mostly it seams to be a good luck superstition that's become a tradition.
As far as Star Trek is concerned, I take it that the two ships mentioned (one of which I consider fictional anyway) I tend to assume they're from ports and colonies with a strong Japanese cultural heritage. Since the early colonist would have lifted off from Earth's surface (rather than embarking in orbit) it stands to reason that the large groups of settlers were mostly from the same region, so it stands to reason you'd get Earth colonies with strong cultural ties to one Earth culture in particular. So by that logic Tau Ceti IV was initially settled by Japanese.