comms
Asking from a communications engineer perspective-
Tower is heard calling the #526 without replies, yes?
I'm hoping that's not due to radio issues as that would be SO 20th Century.
Failure to receive or listen to taxi clearances would seem to be the highest risk to success during this phase of flight.
So is it a rarity for a crew not to hear a call like that?
Are there other factors that enter in?
And yes, a simple red light seems like a good idea to me. Not a total solution but another slice of cheese with not many holes.