A Traffic-Sign Recognition (TSR) system uses cameras and image-processing software to recognise various traffic signs.
The car uses this information in traditional vehicles to display information or an alert to the driver, such as if the system determines that the car is travelling faster than the posted speed limit.
In autonomous vehicles it can be used to determine the speed at which the vehicle will travel, among other things.
At the moment most systems are only able to recognise a limited range of signs due to the challenges associated with computer software attempting to interpret the huge range of road signage displayed around the world.
This will rapidly change though, as road-sign recognition is one of the most important factors necessary for autonomous driving so is being steadily worked on by numerous organisations.