A vanity URL is a short link to your Facebook Fan Page, for example, http://www.facebook.com/signupto
You can register your short URL at Facebook.com/username. This page allows you to set your own personal URL as well as the URL for any page you manage.
You can only set your URL once, so think carefully about what to use. We chose ours as signupto (as opposed to signup/signuptech) because we use the same for our Twitter account. Best keep these things consistent!
Once you have your URL why not include it in your newsletter or send out an email campaign to let people know.