Andrew Gideon wrote:

Yes. They'd also need to identify the marshal amongst the passengers, as
you noted. However, relying upon these "secrets" is relying upon something
called "security through obscurity". It doesn't work in the long term.

It doesn't have to work in the long term. It has to work for the duration of
that flight.

George Patterson
Great discoveries are not announced with "Eureka!". What's usually said is
"Hummmmm... That's interesting...."