In the traffic signal example, the lights can be programed, with a whitelist of all IDs which are allowed to change the signals, and where the signals can be reprogrammed, to mitigate cloning.

I presume that any sort of illegal device which modifies car-to-car communications for other than safety reasons would not be tied to an id registered to a specific car. If only because those devices may need to be replaced, making a registration headache.

I also presume that there won't be a global upload/download of the message traffic for centralized analysis, so who do you think will be doing the recording and analysis?