LYRV 2022-2023 Snowbird Trip Thread
I have found that it's the honor system in most places, and as you say, just show up and camp. Occasionally a ranger will show up and enforce the rules, but that is generally few and far between a happening.
Rangers are responsible for vast land areas and don't have time to check on campers. Usually, if they do, it means there have been problems with people squatting on the land and getting complaints about it.
Some busier places, like Quartzsite, for example, will have volunteers that manage a camping area. One called Plomosa Road BLM comes to mind. Volunteers usually manage check-in locations in January and hand out 2-week permits. They get posted in the camper window for a drive-by ranger to see.