IF I stuck STOP signs every 5 meters, a human will realize that they can be ignored and its a prank. Unless autonomous cars are trained for precisely this kind of malice they will fail.
IF someone decides to hunt autonomous cars, there really is nothing in their models which will save them. They aren’t designed for predator/prey dynamics.
When you open up technology to the world, you open it up to the best and worst of humanity. There is no way fully autonomous cars survive.
The bar for malice will be significantly lower, and it's the car that will be at fault, not the person with the stop sign.
Can I walk around with a stop sign on a pole? Why not? It's not an official street sign. We don't have laws that I know of against carrying around homemade stop signs, I don't think, because any competent driver is able to identify that they aren't official.
Maybe I should get a backpack with a stop sign on it, for when I'm riding the bike.
Driving data is inherently culture biased on the most frequent scenarios. But this is a data set with many outliers.