Although it may be unfair to London (which I know is sunny on occasion), this shot struck me as being the definitive iconography shot.

The London Underground roundel of course, for the station with the distinctive London-like name Charing Cross (notwithstanding that there are also Charing Crosses in Glasgow, Lahore Pakistan, Ontario Canada, Bendigo Victoria and in the suburb of Waverley in the eastern suburbs of my very own Sydney, but this was the original), the statue of Nelson's column, and of course the grey, cloudy sky. And the old-fashioned light pole.

In summary, I thought it gave off the perfect London vibe as the day slid toward dusk at 4:15 in the afternoon.