He's talking about a rubber strap that is attached to a lug nut on the trailer wheel. Its long enough that it sticks out and hangs outside the tire. You can look in the mirror and see it that way you can be sure the brakes released and the wheels are turning. Sometimes the brakes freeze to the drums in the winter and if its slick and they dont release, you can be going down the road with a set of duals not turning. I have seen it happen. Even though the road is slick and icy, its still possible to make some big flat spots on the tires and ruin them.
Nope, Im not that smart, just did a quick search and copied the reply.
Did I get it Mike?