In a time before I had any awareness of international security concerns, I was taking photographs of an airport and the planes taking off from an adjacent abandoned industrial lot. To my surprise, the federal police showed up and ask what I was up to. Turns out explaining that you're taking pictures of something because it looks cool is not going to cut it, I guess it's shallow enough of a reason for it to be suspicious. They asked to see my photographs, because it was all sunset silhouettes I think they were satisfied I wasn't trying to gather intel on the airport and they went on their merry way.