Sam Spade was created by Dashiell Hammett in his 1930 novel, *The Maltese Falcon*. Sherlock Holmes was created by Sir Arthur Conan Doyle in his 1887 novel, *A Study in Scarlet*.
Both characters are protected by copyright law. Since both authors have been deceased for a long time, their works are now protected by copyright term extension laws, which extend copyright protection for works created before 1978. This means that their works will remain under copyright for many more years.
Public domain refers to works whose copyright has expired, allowing anyone to use them freely. Since the copyrights for *The Maltese Falcon* and the Sherlock Holmes stories have not expired, they are not in the public domain.
However, there are some caveats:
* Certain adaptations of these characters may be in the public domain. For example, early film adaptations of Sherlock Holmes stories may have fallen into the public domain.
* There is a debate over the ownership of Sherlock Holmes's character and stories. Some argue that the character is too iconic and recognizable to be fully owned by anyone, and that his basic traits are in the public domain. However, this has not been legally established, and the Conan Doyle estate actively enforces its copyright on the character.
It's important to remember that copyright law is complex, and it's always best to consult with an attorney before using characters or works that are not in the public domain.