Also - if someone is at the side of the road waving a mobile phone, and a "car" swerves illegally into a bus lane or a bike lane to pick them up (as often happens to me - I had a near-miss [near-hit?] again yesterday), then it's a good bet that the car is a mini-cab/whatever. And it always turns out that that is the case when you look closely and see the sticker in the window. So that's another way of distinguishing private-hire cars from ordinary cars...