Q: Match the film actor with the movie in which he starred.
Answer: Personally, I'd wager that Dick Powell was the fellow the stamp designer had in mind. Powell played Marlowe in one of the best Hollywood adaptations: Murder, My Sweet (1944).
Robert Montgomery's Lady in the Lake (1947) is unique for its arresting first person perspective. Both Bogart and Mitchum played Marlowe in versions of The Big Sleep. Mitchum also starred in an adaptation of Farewell, My Lovely in 1975.