San Francisco: Burritt Street
For more, see: The Maltese Falcon: The Scene of the Crime
From The Maltese Falcon:
"Spade turned from the parapet and walked up Bush Street to the alley where men were grouped. A uniformed policeman chewing gum ... put out an arm and asked:
"What do you want here?"
"I'm Sam Spade. Tom Polhaus phoned me."
"Sure you are." The policeman's arm went down. "I didn't know you at first. Well, they're back there." He jerked a thumb over his shoulder. "Bad business."
"Bad enough," Spade agreed, and went up the alley.
Half-way up it, not far from the entrance a dark ambulance stood."