It doesnt matter "who" approaches you. It matters what the regs say. The FAA can find out many different ways of people in aircraft doing stupid or dangerous acts or violating rules/regs. The average person would call the police who report to FAA, etc. Simple chain of events. Any pilot would most likely call you in as well for being unsafe and breaking the regs. Yes I am trained in the FAR/AIM as I also hold a private pilots license and yes if I saw you land in a non emergency situation on a public road, I would probably call you in for being unsafe and breaking regs. If you said it was an emergency landing I would also call you in as the FAA should be aware of that and I would be obligated to report it. If I were flying and I saw you land on a road, I would call ATC and report you for fear of it being an emergency. If you land in fields of people you know and are authorized to do so you would be fine as long as you dont break regs. Dont be surprised if someone doesnt call you in the first few times concerned that you may actually be in an emergency situation. You keep asking the wrong question of "who" enforces it when the question to ask is what are the regs I would be breaking. Like I said, there are many many ways for the FAA to find out and many of those are the average public calling in low flying aircraft. Ive been called in a few times.