Advertising posters line the route in and out of most tube stations. Occasionally, you will see a piece of strategically-placed chewing gum (on someone's nose or such like) and at other times a small sticker protesting.
Ascending the escalators at Angel yesterday there were posters promoting cosmetic surgery at HarleyMedical which made me frown. That is until I saw one displaying a hand-written label: "self-esteem cannot be purchased". That made me smile.