I can tell you for sure that he's wrong on that one. Paranoid delusions. For one thing, any and all of one's medical information is strictly private. No one is under any obligation to divulge anything regarding the medications they take, or any medical conditions or illnesses they have. It's actually illegal for ANYONE to share ANY of your medical information with anyone else without your written consent. And NO ONE needs to know that you participate in a state sanctioned medical marijuana program, EXCEPT THE STATE. Whether you're a grower, caregiver, or a patient. That's NOBODY'S business but yours, and/or the patient's.
For another thing, "display the registration card at the marijuana grow site" does not mean it must be posted in public view. It can be displayed ANYWHERE at the grow site. "Displayed" means out in the open and easily viewed. Not hidden, like in a file cabinet, drawer, or underneath of anything. You can have it laying on the counter, shelf, table, floor, or hung on the wall(or on the ceiling for that matter), inside or outside. To display it outside for all to see however is definitely not required and is, quite frankly, asinine.
I keep mine hung on the wall, in plain view, in the first room you enter at my grow location. Directly upon entering you need only look to your right, and there it is on the wall posted at eye level for easy viewing. I've had police in there on several occasions, and they've never had a problem with the way I've displayed it. In fact, they've never said word to me about it, or the fact that there were marijuana plants growing in plain site there too. They've always acted as though it weren't even happening. Like the shit was invisible.
(3) A person who has been issued a marijuana grow site registration card under this section must display the registration card at the marijuana grow site at all times when marijuana is being produced.