One of the most popular trails in the world is the Appalachian Trail, and many books will focus their time on it. So, if you happen to be interested in actually hiking it yourself, then you may be curious to see if you have to register.
The Appalachian Trail is monstrous and spans over several national and state parks. While there is a voluntary registration, you should use it to pick your starting dates and such. Of course, you also have to be careful as you may access parks that require specific permits.