The problem with that, at least on my experience with iPhone, is you can only get the authentication signal after you’ve already hung up. The only thing I see is a small checkmark next to the “location” of the call in my recent call log. I can’t find any indication of a stir/shaken status in the active call screen.

So asking people to take the step to confirm the call is legitimate won’t work- they can’t tell until they’ve already terminated the call. It’s useless for purpose imo.