People are more wary of "suspicious" activities today than they used to be. People also have different perceptions of what activities are "suspicious". A group of tourists taking pictures around a well known landmark is unlikely to draw attention but one person photographing a relatively anonymous structure at an odd hour of the day is more likely to seem suspicious to a lot of people. Some people probably don't know the difference between a large format camera on a tripod and a rocket launcher.

I can remember being detained by FBI agents at the local Federal Building parking lot once because of suspicious activity. This was around 1980 or so. I was doing a photo stake out for some local bigwig being tried on federal charges. I was suspicious. I was standing in a parking lot in the rain wearing a hat and raincoat with two cameras around my neck and a bag over my shoulder with a walkie-talkie attached. I looked suspicious even to myself.