I flew LHR - CPT in a 340 with a missing winglet, the captain announced very soon into the flight that 'those of you on the left hand side may notice the unusual appearance of the wing tip ....' and went on to explain that it had been damaged in a taxiing incident, that flying without it was perfectly safe and incurred a slight drag penalty, and that it would be replaced at the earliest opportunity. It was very well handled in humourous and professional manner.