"Rear doors either do not have an emergency release" - you mean like every coupé ever built? Since when were you protesting coupés? Rear doors not only do not have to have manual releases, but don't even have to exist.
"lack and/or ambiguity of signifiers" - the front manual release handle is not only not ambiguous, but is far more prominent than the electric release button, so most people with no experience with the car pull it instead of the button.
It's also, in all this, noting that modern cars have crash sequences. A crash is detected either (ideally) immediately before, or during its occurrence. A wide range of events are triggered, such as brakes, airbags, etc... and among the things triggered is *unlatching all the doors for easy egress* (the specific details depends on the door design - you want the door easy to open but not to pop out during the crash itself). Now, things can go wrong - the prime characteristic of a crash is that it mangles your car, and this can jam doors shut or cause other problems. This is why the Jaws of Life exists. But prepping the doors for egress is something that cars at least try to do during a crash.