Once a contributor has read the notice, they may prefer not to view it any more. If they have cookies enabled, they can dismiss the notice using the "dismiss" link next to the text. This will work whether they are logged in or not. As long as they don't clear the cookie, the notice will remain hidden.
To reset the notice, and make it visible again to all (for example when an admin has put up a new notice) the number in MediaWiki:Sitenotice id needs to be increased by one. If this page doesn't yet exist, it can be created with a starting number of 0. The new notice can be dismissed after reading in the same way as the last.
Use a site notice for important or temporary messages updates only. If a site notice used too often, regular users to your wiki might begin to ignore it, which makes it harder to get the really important notices out. When not needed, clear the message as mentioned above.
Keep site notices short and sweet — one or two lines of text with links to more extensive information is best.
Keep page load times fast by avoiding images, polls, DPL, or other extensions in the site notice.
Consider whether to use the MediaWiki:Anonnotice, which allows you to talk only to users that are not logged in, or to show a different message to that group.
Sitenotice messages should generally not be signed.
The sitenotice allows most wikicode. For example, code linking to a certain page will turn into bold text on that page. However, the Sitenotice is known to sometimes cache for pages other than those it appears on. If you encounter this bug, to prevent a link to a page becoming bold text on every page, add a null anchor point. For example, instead of: