After you've registered and signed in with your Yahoo! ID, go to the Options screen by clicking the "Options" link. It should be located on the same gray Welcome bar near the top of any Message Boards page.

From the Options page, you can choose to turn the Profanity Filter on or off. You can also do this at the bottom of every Message List page or in the lower-right corner of every message.

From the Options page you also choose your Profanity Filter settings—choose between either weak or strong filtering, and select your display options.