I realize it has been 9 years since this thread started, but I just came across this question after re-reading the Falcon, earlier this week.
The Cuban composer Eduardo Sánchez de Fuentes wrote the song, En Cuba. In 1923, the American composer Frank La Forge published an arrangement of the title for piano. You can purchase a copy of the publication on Amazon, here.
Since Hammett’s original short stories, The Whosis Kid, and The Gutting of Couffignal, from which he drew many of the characters and plot points when writing The Maltese Falcon, were published in 1925 in Black Mask magazine, it stands to reason that the song would have made it to Hammett’s ear at some point in those two years since its publication in the United States.
By 1929, when Hammett began publishing the novel in Black Mask, my guess is the song was fairly well known, but not commonly performed or recorded. I’m still hunting for a recording; I’ll keep you folks updated.