Original: Every editor's default signature (defined by MediaWiki: Signature) will display when ~ ~ ~ ~ is typed.
Simplified: To sign a post, type four tildes, like this: ~ ~ ~ ~. To type the username only, type 3 tildes: ~ ~ ~, and this would appear: Example. To type only the date, type five tildes: ~ ~ ~ ~ ~, and this will appear :00:00 01 January 1000 (UTC).