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.
He took down the great book in which, day by day, he filed the agony columns of the various London journals. â€œDear me,â€ said he, turning over the pages, â€œwhat 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.â€