What does this sign indicate?

• Drivers must stop completely and yield the right-of-way if necessary before proceeding.
  Explanation:

  "This sign requires drivers to come to a complete stop at the marked line, crosswalk, or intersection. Drivers must check for oncoming traffic and pedestrians, yielding the right-of-way when necessary before continuing safely."
• Drivers must slow down.
• Drivers may proceed without stopping if no other vehicles are present.
• Drivers may proceed without stopping if no other vehicles are present.