The 2024 sequel: Swap the clipboard with a tablet with a rugged case and youre allowed to just ignore anyone that does happen to walk up.
Just keep staring at the screen and tapping. If they persist, look at the screen, then look 50ft away, then the sceen again, then walk to that spot you were looking at. They will give up.
One time, I had just gotten an EMF meter. And I was curious, so I went, dressed in business casual, to the local Whole Foods, with a clipboard, and my EMF meter. I mapped the whole store, and parking lot. No one, not a soul said anything to me.