Boat trailer license plate question

Saw one going down the road with the license plate mounted on what looked like a little 90 degree aluminum thing that was bolted to a small clamp. He had that clamped onto his power pole. I guess he would just toss it in his truck when the boat wasn't moving.

Seen a bunch of skiffs with their plates mounted to clips that snapped onto the poling platform.

I bolted mine with lock nuts. The idea being most plate thieves have only a screw driver and not a wrench.

I think "legally" you're supposed to have it on the trailer, but I know several guys that just carry it in their trucks and have never been stopped.