Mike, do what I did... call the police.
I was hasseled by a security guard because I was taking a picture of "his building." He told me I couldn't take pictures and I, very calmly, told him I was on public property taking a picture of a building that was viewable from said public property. His reply was that he was going to call the police, so I whipped out my cell phone and dialed 911. When they answered I told them I was being harassed by a security guard while taking a picture of a building from a public sidewalk--then I handed him the phone, he said "uh huh" a couple of times, apologized and then went back inside.
Too bad the picture I took sucked, but the afternoon was fun