This clip is from the CBS 1949 Studio One production of the Dashiell Hammett short story “Two Sharp Knives.” Hammett’s cameo is that of the character Slim, not listed in the cast of characters. This is the only film footage of Hammett I’ve been able to find. I’m sure there must be more.
I had a short communication from Dashiell Hammett’s granddaughter, and she believes this is the only known recording of her grandfather’s voice.