For the most part, bear spray is 100% legal across the U.S. (Even in Hawaii where there are no bears). See the attached article for more information.
I only carry it if I'm going to an area with a history of bear attacks. I'd really recommend it if you're going to locations that have grizzly bears.
As for carrying it concealed or in the open, there are no rules about it, but just make sure you can access it very quickly if you encounter an aggressive bear.
If I actually had to use it to deter an overly aggressive bear, I'd notify game and fish department of the state I was located in. The only exception would be if I was in a national park, I'd notify the park rangers.
Bear spray info