It kinda sucks, though, to put the responsibility for this on the first responders, who already have enough to do dealing with the emergency.

As a general principle, one can imagine special signals relevant to autonomous vehicles. But there's probably something of a chicken and egg sort of thing and I have problems with a lot of processes being required to deal with early adopters of this sort of technology.

There are going to be times when someone is legitimately responding to an emergency and doesn't have a stop sign handy.

And there are going to be a lot of pranksters who do, and will use them to mess with so-called self-driving cars.