1. When you create a game, there is an option to select rated or unrated.
2. If you are looking for a new game on the "open invite" list, there is a column on the page that shows if the game is rated or not.
3. If you want to check on games you are already playing, go to the "my games" page and click the "info" link on the right-hand side for the game you want to check.
(It is always a good idea to check the "info" link on any new game added to your games list to make sure it is set for the right parameters. By doing that, if it isn't what you want you can delete it right away.)