Time to stir the pot again. This is coming from a State Trooper so it has a different perspective. The way it is described, the TX farm plate law for trailers sounds like the same as WI. Farm trailers cost a fraction of regular trailer plates and are called "restricted use". Farm truck plates can be used for personal use but farm trailer plates are farm use only.
As far as the safety chains issue, I have never even considered citing someone for not having the chains crossed. Nor have I ever stopped someone for not having them crossed. I will advise people that I have stopped on what is required and why. I get more worried about the guys that don't have adequate safety chains or worse yet, the ones with NO CHAINS. Those are the guys that get tickets. For the most part, farmers do a pretty job getting chains hooked up and having good equipment. Scrap haulers (at least in my area) are a different story. I've stopped plenty of rigs going to the scrap yard where the whole **** rig, truck, trailer and load should be left at the scrap yard.
I had a co-worker of mine was badly injured by a ranaway trailer. He was operating laser in a crossover on the interstate when a bumper hitch cattle trailer broke loose. It t-boned his cruiser and he ended up with a broken vertebrae. So yes, things can happen.
Another two issues not yet discused here are trailer brakes and trailer lights. In WI, when a trailer and load exceeds 3000 LBS, the trailer has to have working brakes. That's another issue I find not only with scrap haulers but others that haul heavier loads. Many times the trailer will be equipped with brakes but the truck pulling it isn't set up for trailer brakes. The lights issue is just common sense. Trailers need to have working lights. I don't like it when I stop a rig and the trailer wiring harness isn't plugged in because there's no place to plug it in...you got some explaining to do.