Well, that's silly, all Signal chats are secret; it's not like group chats are public.
"The group's chat description identifies itself as a 'clandestine' group and new members are warned to 'remember the first rule of Fight Club.'"
... Well, then.
I previously worked at an insurance company some years ago. Back then the company was complaining that flood maps were something like decades out of date, and that was irresponsible to let developers build and sell homes to unsuspecting homeowners who had no reason, or even a way, to know they were in a flood plain.
I suspect nothing has changed in the intervening years.