I hauled ladders and equipment for my siding business for 25 years. I never learned the rules until after the business was shut down. The above posters are correct but in those 25 years I only got pulled over once by cops and it was for speeding. They gave me a warning because my straps were old and didn't have legible load ratings sewn onto the straps....who knew I needed that? What it comes down to is if you are a licensed business you are supposed to know the rules. Even if you aren't told when you get the business license you are responsible. I worked for 20 of the 25 years as a proprietor which means unlicensed business so the fines are a lot less than a licensed business. The fine I could have got for the straps was over $1000.00.....I went and bought new right away.
I've found one of those magnetic lights on the side of the road and with a little repair am using it myself, but I won't trust just the magnet, I tape it as well.
For a flag, I'll use anything if I don't have a proper one, a shirt, a plastic bag, whatever. I used red 2" tuck tape many times, folded over on itself so there was a "tail" flapping behind for about three feet. I figured that was more likely to be noticed by someone following and therefor safer. I don't know how legal it was tho. Like I implied, I never got pulled over for improper flagging in 25 years, but I also put in an effort to have something to warn people.
More important, IMO, is how the load is secured. I have lost a few things over the early years and learned pretty quick what was needed and what wasn't. Always take the time to tie down a load, even if you are just going around the corner.....trust me on this!
Richard