Many years ago I was once detained by the army for shooting (film!) in woodland close to their base. I had no idea the installation was there, was only seventeen and they eventually let me go. However when I returned home many hours later via various friend's houses, there was a military vehicle waiting at the top of my parent's street, so they clearly took such events seriously.
Last year one chap I know was questioned for using his mobile phone at a railway station! He didn't have his reading glasses and had to peer at the keyboard and they assumed he was taking a photograph. Strange times we live in.