To me, London Black Cabs have always SCREAMED London to me.
I remember as a very little girl living in Surrey, coming to London to spend some time in my Dad's office (I think it was near Hatton Gardens...I think!) and going to lunch in a London Black Cab. It was VERY exciting. The cabs had tinted yellow back windows which made London look amazing! (remember, I was about 5 or 6) and they were big and noisy and...well...Black!