Apart from flashing red lights, what indication will vehicles be given that a school bus has stopped for students?

• You will see flashing amber lights.
• You will see a stop sign extended from the right side of the school bus.
• You will see a stop sign extended from the left side of the school bus.
  Explanation:

  "You will also see a stop sign extended from the left side of the school bus."
• There will be no other indication.