I guess I would use my usual trick when people tell me something is illegal. I'm also a photographer, and in that discipline, I've been approached several times and told what I was taking pictures of was illegal. It really depends upon how involved you want to get with the person claiming the illegality of what you're doing. I was accosted on a street in San Francisco a few years ago by a security guard who was telling me taking pictures of an interesting building was illegal (it was a bank). I asked him if he could cite the law, so I could look it up. He stammered a bit. Then I asked him where the signs were that indicated no photos were to be taken. He stammered more and started to talk loudly (a sure sign of defensiveness). I kept calm, and kept smiling. Finally he said, "We'll call the police if you keep taking pictures." I was in the mood for an argument, so I replied, "Yeah, that's a good idea. Let's get a cop here to explain to you that this is a public street in a tourist town, and that taking pictures are not only permitted, they're encouraged." He said, "I'm calling the police," and went inside the bank. I replied, "I'll wait." I took more pictures, and then walked down the street, looking for more shots. Never saw the police SWAT guys who the security guard obviously hoped would show up. It was a bit childish on my part, but dang, it was satisfying. But back to the thread. If you are told something is illegal by a private citizen, act a little confused and politely ask which law you're violating. It's more than likely the conversation will come to an end soon after that.
