When the header message is dismissible, a close button appears beside it so members can hide it. The choice is saved in the member's browser, so the message stays hidden when they come back until their cookies are cleared. If you turn the option off, the message is shown to every visitor again.

1. Log in to your Website Toolbox account.
2. Click the Pages link in the left navigation menu bar.
3. Click Header.
4. Turn on the Dismissible option.
5. Click Save your changes.

The header message appears below the main navigation menu on every page of your forum. See How do I edit the header? for adding the message itself.