You will notice a message telling you that you are not registered. It's quite simple to register... Go to the Players page and click on User settings. That is the menu where you can change your details and also you can request for a confirmation email to be sent to you.
Registering is not mandatory, but it would be polite if you did so. More than that, registered accounts will receive a daily (game monthly) amount of coins on the owned players, given that they have been active in the previous day and that they own an account at the local goldsmith!