The door to Blane's hotel room has a deadbolt knob above the doorknob, but no corresponding bolt or plate on the edge of the door. Same goes for the key lock below the doorknob. This is a frequently-seen shortcut by set carpenters.
When Blane gets off the train at the second station, a moving reflection of the boom microphone is visible on the glossy paint surface of the rail car to the right of the doorway.