Intellectual property is an enormously complex legal area (in which I have passed exams!) Basically there are two international conventions organising design rights and copyright in the world. Most of the world follows one, the USA and some other countries follow, and then there are countries which don't bother about any such issues.
That's the law. well known brands have breached patents before now and been caught out and made to pay millions. Words etc ..well, it's easy to compare a couple of texts to see if they are the same.But designs are tricky because they are so hard to define.
Many people don't care if they copy a design (that's why knock off designer stuff is a flourishing industry) but at the same time, if you have pride in your product you won't want to be copying. I know that there are copies of some of my things out there (a six strand white pearl top drilled necklace for a start) and I could kick Hisano for getting the gemstone inlaying thing out there literally a day before I was photographing my version - but at the same time someone somewhere may well be looking at Hisano's and thinking 'oi..that's my original idea)....
But I'm not going to list the earrings I made with inlaid gems because I am prideful of what I do and respectful of what Hisano does. So I have a pair which will be for me. And that's it.
So yes, you can knock off any designs, but then you will be known as a knock off merchant.