lol the idea that any enforcement to that degree exists in the US is a fiction.

The fact that you used the term "enforcement" here makes me presume you are thinking of criminal consequences. But the grandparent comment talks about civil liability. Certainly if there were injuries at this intersection and they knew who had altered the signage, attorneys would argue liability on the part of the vandal. They'd get settlements if not win cases this way.

In addition, if there were serious injuries here you should also expect some criminal consequences. But if your point was to suggest that they won't hunt you down just because someone said there was mischief here, I tend to agree.