Good way to let the reader know the story is set in 1911:
- Have a character mention the theft of the Mona Lisa from the Louvre
Bad way:
- Have a character think about their plans for the next few years, and by golly are they glad wars don't happen any more
@Louisa Big 1913 energy.
(See also: The story is set in 1939 because someone scoffed something about "the war to end all wars!" at a newspaper.)