In brief
The camera classifies visible signs and presents them to the driver.
Useful to know
Bosch's traffic sign information system uses camera and recognition algorithms. It can display restrictions and other signs on the display, including reporting additional signs according to implementation. [1]
This is different from a stored speed in a navigation map. The two technologies can be combined, but they should not be considered the same. In case of a wrong or missing indication, follow the actual road signaling. The presence of a number on the dashboard does not mean that the system has correctly read every condition and every sign in a complex road junction.
Sources
For further detail and to check the information: