You could be Acme Corporation
in Nebraska and legally own that
corporation in that state, but there could be another Acme Corporation
in every other state, and every one of them is legal until you win a
lawsuit proving that they are trading on the commercial interests you
own.
When you really get protection is when you use that name, and
therefore when you find somebody else using it you can prove that you
had it first, so they are trading on your name.
There are lots of
McDonald's restaurants around, and McDonald's can't stop them from using
that name if they had it early enough, and especially if they aren't
pretending to be a fast foods hamburger joint. The attempt to confuse is
very important.