Two schools of thought here. Be polite, ask permission, don’t rock the boat. Or…. shoot first, ask questions later. I lean toward the latter, as once you press the shutter you’ve got the shot, for better or worse. The slightest pause can mean losing the image that first caught your eye. It’s often the impulsive photo that works for me. The Paparazzi know this, it’s in their blood, instinctive. It’s not a good way to make friends and you might even get your butt kicked if, say, you decide to shoot a government building. That’s why having an Eye-Fi memory card makes sense. The shots get wirelessly transmitted. So if the goons crush your camera, the picture survives. Even if you don’t.