A sign of strength, or a mark of sadness? A quick check of popular quotes about fake smiles shows that opinions are divided.
Psychologist Paul Ekman has become famous for his systematic way of analyzing micro-expressions: involuntary marks of emotions in the face that give away how a person really feels. His analysis on smiles is presented in the classic article "Smiles When Lying", co-authored with Wallace Friessen and Maureen O'Sullivan.
Based on Ekman's work, advice on how to distinguish a real smile from a fake one is plentiful on the internet, and there's even a test you can do to check how good you are at it.
Others are more interested in how the fake smile feels inside - and what incessant fake smiling does to a person. The fake smile is an essential element of the face service workers have to put on for their customers. Arlie Hochschild in her book "The Managed Heart" argued that this can lead them to become alienated from their true feelings.