What can I use as a trail name?
All trail names must include at least one letter or number.
And, of course, you cannot use a trail name that someone else has already registered, or a variation of such a trail name.
The most requested punctuation mark asked to be allowed is the ampersand (&), but that character is specifically not allowed since it's a special character used for HTML text and the encoding issues are just plain messy. You can ask, but it will likely never happen.
You can change your trail name from the Account Info page. The only effect this has is that your trail name is changed--you still have all of your plants, finds, message board posts, etc.--everything is the same as before, except that your trail name is different. For a month, nobody else will be able to use your old trail name, and for a time anyone who runs a search for your old trail name will be able to see that you changed it. Other than that, though, it's the same as if you had the new trail name the entire time.
Keep in mind that this is the way other letterboxers will address you at gatherings, events and whatnot. It's helpful if the name you choose is actually pronounceable.