I've looked at the vehicle code and some sections like tires have a "when operate on the highway" in them. However, some of the a-hole cops/rangers will enforce that. I've had a few law enforcement types mention my signals and mirrors, but I have never been cited, yet.
Now a sticking point is that all the lighting and the mirror must be DOT approved in order to be truly legal. I have a DOT headlight, but that is about it. The HID inside the headlight is not DOT compliant. Neither are my tail light or turn signals. My mirror is one of those foldable Acerbis jobs and it is too small to be compliant.
I do have DOT tires. I have been told on more than one occasion not to hit the pavement by law enforcement while on the dirt. That seems to be the most common thing looked at.