APA (7th ed.) Citation

Project Gutenberg & Doyle, A. C. (2000). The Sign of the Four. Project Gutenberg Literary Archive Foundation.

Chicago Style (17th ed.) Citation

Project Gutenberg and Arthur Conan Doyle. The Sign of the Four. Salt Lake City: Project Gutenberg Literary Archive Foundation, 2000.

MLA (9th ed.) Citation

Project Gutenberg and Arthur Conan Doyle. The Sign of the Four. Project Gutenberg Literary Archive Foundation, 2000.

Warning: These citations may not always be 100% accurate.