School busses, at least in my region (and it appears in the image this is true as well), have flashing red lights at the top to indicate that traffic must stop. The stop sign also comes out, but it’s the flashing red lights that should be a dead giveaway to anybody driving.

In my region, they also have flashing yellow lights before they stop, indicating that traffic should slow down and prepare to stop.

Edit: and I should add that the expectation is that traffic stops in all lanes, both directions. Being in a different lane or off to the side makes no difference.