I think that is just regular road grime from the looks of it from those studs in this pic but I could be wrong. Loose lugnuts are often caused by Magilla gorilla with the impact gun on full blast elongating the studs and not taking the time to torque them which may be the case here.
Looks like everyone else explained. I was taught that with my first local job 17 years ago. California put me oos for one rust trail. TA had to road call and torque em all down.
I am. God it took you guys long enough. OK yes it is a sign of low torque or loose nuts, but it isn't about the rust itself, I was hoping someone would point out that the trails were going outward indicates water behind the nuts were leaking past the nuts itself, hence the spinning effect on the wheel. The broken one, it is a violation but more likely than not if a cop saw it without a L1, it would be passed off - yes I have had this happen a few times. The reason I would be mainly concern is that it is sheered off, not just broken. I have had a bunch of broken studs on trucks thanks to the idiots with impact wrenches putting 600lb pounds on the nut and stretching it to the point it will break.
You are not correct..the amount of threads showing or visible has nothing to do with the torque load on the wheel nuts. As for the rust..nothing to do with the torque on the nuts either. If you have ever looked at, or inspected a wheel nut.. before installing, it has a washer built on the nut that can actually turn on the nut itself. Even at proper torque there is a groove where they are put together. Salt and brine, or plain water can collect and create little rust trails over time.
Did they check the torque before they actually move any of the wheel nuts. I would have had the officer come out to prove him wrong. Politely of course. Not all, but some officers know just enough to be dangerous. One tried to tell me one time my 5th wheel lever didn't have a safety catch.
How many horns do you hear blowing in a big truck stop between 0500 and 0700? Can't do a full pre-trip without testing your horns!