How vulnerable are road sign cameras to, say, someone sticking a vertical strip of black electrical tape to make the 50 appear as a 150?
Is there any cross-referencing to an onboard GPS database? GPS-based speed alerts are a feature of base-model Hyundais/Kias in Canada, so it doesn’t seem to be too far of a stretch for a failsafe.
I don't know about 50 to 150, but someone near me appears to have put up their own speed limit sign and the font is slightly off, so my car sees it as 75 instead of 25 (and fortunately doesn't set itself to it, but helpfully gives me a single-button way to set my cruise control to match).