Thanks everyone (you too, Andrew). This is a picture that echoes HCB's dictum: "It's always luck." But he added "You just have to be receptive, that's all." So I guess I can take credit for being receptive.
As Stamper guessed, it was in a mall, as was the last one I posted. I was on the second level and peered over the railing and saw. . . this. I had about five seconds to focus, frame, and shoot, because three people were walking toward the frame I wanted. It's cropped. When I saw it I knew it had to be roughly square for the projected shadows to work, and I was shooting with a four-thirds camera.
Generally speaking, Slobodan's right. U.S. malls aren't any happier to have you shooting pictures in them than, as Stamper pointed out, are Scottish malls. But the situation is a bit complicated. A lot depends on what's in the mall. If everything is retail and food, they can keep you from shooting pictures, but if the mall also is a gathering place for, say, a mime performance, or something similar, you may be home free. As Slobodan also pointed out, about all they can do is tell you not to take pictures, and ask you to leave if, after the warning, they catch you at it. I always carry my E-P1 with its fairly big Leica lens, and nobody ever has tried preemptively to keep me from shooting. I always look around to see if there's a guard in sight before I raise the camera and shoot. Now that we're in a recession and the malls are saving money, there are a lot less guards to look for.
Seems to me that trying to keep people from shooting pictures in malls and museums is asinine now that, as Slobodan pointed out, we all carry phones. My Samsung 4 GE has roughly an 8 megapixel camera, which is a lot more camera than the 3 megapixel Casio, the 4 megapixel CoolPix, or the 5 megapixel Olympus E-20 with which I shot some of my favorite pictures.