I was wondering what will happen when somebody places a fake speedsign, of 10 miles per hour on a high way. Will a autonomous car slow down? Is this a current issue of autonomous cars? 
What will happen when you place a fake speedsign on a highway?
self driving;cars
https://www.technologyreview.com/s/530276/hidden-obstacles-for-googles-self-driving-cars/Googles cars can detect and respond to stop signs that arent on its  map, a feature that was introduced to deal with temporary signs used  at construction sites. But in a complex situation like at an unmapped  four-way stop the car might fall back to slow, extra cautious driving  to avoid making a mistake.It's highly probable they would slow down with current technology, as they can detect temporary signs and are designed to use slow speed in complex cases.and if it was a true temporary sign (road repair etc... ) how can it make the distinction? It probably would be worse to ignore a slow down sign than slow down at a fake one.IMO, the problem there is with the joke in the first place, as some humans might slow down too.