There's a wonderfully ironic scene in the movie Atonement.
English troops are about to be sent to France—to their eventual Dunkirk—in the opening days of World War II. Robbie (James McAvoy), recently paroled in return for military service, runs after a bus carrying Cecilia (Keira Knightley).
On the rear of the bus is this Guinness advert:
Have a Guinness When You're Tired
Vanessa Redgrave is on screen for only a few minutes—at the end of the film. And, simply put, her performance is amazing.