Newer cars like my accord use a camera that looks for speed limit signs. What's funny is it's not perfect and sometimes will read a random sign and tell me the speed limit is like 100mph on a 35mph road.
Yeah, those systems have fun issues around elections here in Finland. Often there is advertisements around roads and our system works with each candidate having their own number. These are usually in nice circles with black text in white background for best visibility...
That can't possibly work everywhere. Here in my state in Australia we have speed signs for the off-ramps where they are clearly visible from the freeway, so you might be in a 100 km/h zone but see a 60 km/h sign off the side that could easily be mistaken for a speed sign for the freeway (it's actually not that great design, sometimes they have a sign saying 'ramp speed' under it but not always)