Use {{notice|type=|subject=|comment=}}

  • type (required), currently supported: historical, under-construction, outdated, user-blocked, archive
  • subject (optional), defaults to page, can also be section, ...
  • comment (optional), any extra text after the default notice text
  • expiry (optional), only for type=user-blocked
  • archivelink (optional), only for type=archive, link destination of current discussion page

For a custom notice, add text as a first paramter: {{Notice|42 is the answer.}}