Dark Passage - Harry's Wagon
After Parry recovers from his plastic surgery in Irene's apartment, she removes his bandages and gets to see his new (Bogart's) face. But he doesn't want to put her at risk and decides it's best to get out of her life. He calls for a cab and tells the driver "Post and Fillmore" - the cab drops him off at Harry's Wagon, a railcar-styled diner sandwiched between two buildings.
Then ... These ad hoc diners were popular at that time. Diner researcher Richard Gutman in his informative comment below explains that this particular one began life not as a rail car but as a purpose-built horse-drawn street food wagon in the early 1900s.
... from the 1947 street directory ... the entry below confirms that Harry's Wagon was indeed a real diner at 1921 Post Street near Fillmore (map).
... and Now, Sohn's French Cleaners currently occupies the setback building on the site of the old diner, re-addressed as 1919 Post Street.
... a similar diner ... Harry's Wagon is long gone but thanks to reader Zach Georgopoulos (see his comment below) we now know where we can still dine today in an similar railcar, the Grubstake, at 1525 Pine Street, which according to their website was a converted railcar from the long extinct Key Line railroard system.
A suspicious detective apprehends Parry in the diner but he gives him the slip and takes off (below).