It's not a secret either.

There is an amber light on the scoring control box above the middle driver's station. Normally the light is OFF.
The light turns ON for 10 seconds at the end of a match (when the buzzer sounds). When the light turns OFF then the scoring controller stops counting.
Also, the light will blink/flash during a match when DOGMA has assessed a penalty for that side (Red or Blue).
Some teams knew about it, some didn't, which is maybe an unfair advantage. If you can see that the other side got a DOGMA (which is not counted in "real time" total on the audience screen, btw) then it might make a difference in your strategy...