Watson reads the newspaper to Holmes and Jabez Wilson

In the 19th century, safe and anonymous communication was achieved via classified advertisements in the daily newspapers.

In the Conan Doyle stories, Sherlock Holmes often turned to them for clues.

Adventure of the Red Circle:

He took down the great book in which, day by day, he filed the agony columns of the various London journals. “Dear me,” said he, turning over the pages, “what a chorus of groans, cries, and bleatings! A rag-bag of singular happening! But surely the most valuable hunting ground that was ever given to a student of the unusual.”

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