Checkpoints and stops for a line following robot

Need help how to put stop for line following robot.

Set a brick in front of it.

Gap in the line?

Or a line across the line, like a T or +.

But usually the layout of the course (including symbols like that as instructions to the robot) is provided by the rules of the competition or the assignment....

edit: so is the question about ideas for demarcating a "stop sign" on a layout, or about how to make the robot stop when it finds such a mark.? Or both?

I remember seeing somewhere a bot that would read coloured marks placed next to the main line. It could be instructed to turn left or right at upcoming branches by reading the different colours. Maybe you could find that project online?

Not always a finish line marker exists:

There seems to be a light barrier only for time measurment – robots pass that line twice.
So either robot can detect the light from light barrier while passing, or it gets a wireless stop signal.

The robot is really fast, does take the round with 3.10m/s on average(!).
I would expect that it runs with 5m/s on the straight segements.
They use a vacuum pump to suck the robot to the ground in order to be able to drive that high speed (that is the explanation for the loud noise you hear during the run (and just before starting!).
It is shown as very first run in this youtube video: