What do pavement markings like an "X" and/or a stop line indicate?

• They mark the approach to a railway crossing.
  Explanation:

  "Pavement markings such as an "X" and/or a stop line are used to indicate the approach to a railway crossing. These markings serve as a visual warning for drivers to be cautious, look for trains, and prepare to stop if necessary."
• They mark the approach to a school bus stop.
• They mark the approach to a heavy vehicle zone.
• They mark the approach to a light vehicle zone.