You do not need to sign up in order to access Pendragon. All account holders have the ability to play on the Pendragon test server. In order to log in to Pendragon, you will need to perform the following:
Open up your C:\Mythic\Camelot folder. Within that folder, you will find two similar icons: Camelot.exe and Camtest.exe. Running Camelot.exe allows you to login to the main servers. If you click on the Camtest.exe file, you will connect to a different login server that will then allow you to enter Pendragon. Once the program launches, proceed to login as normal. You may also right-click the Camtest.exe icon and make a shortcut to it on your desktop so that you may more easily re-enter the Pendragon test server in the future.