See Bendy (disambiguation) for other related uses.
In Chapter 1: Moving Pictures, the whistle plays from the auto-played projector of the theater as soon as Henry enter this location after placing all six items on pedestals from the break room and get the ink flowing.
In Chapter 2: The Old Song, first 11 seconds of the track itself can be heard when going backwards into Ink Bendy's pool area (but not entering normally, as to not incur Ink Bendy's arrival), and going up to the door, Henry can hear the Ink Machine running and the whistle.
In Chapter 5: The Last Reel, at the beginning after Henry wakes up in a prison, Allison can be heard humming the tune before Henry states that he knows the song. From the post-Chapter 5 epilogue, where it takes place in the apartment, Joey Drew is heard whistling the same tune before meeting him in the kitchen.
Joey Drew Cartoons
The song is played for the Bendy cartoons shorts' intro title cards. The song itself has a similar melody played with big band instruments in older, vintage-styled themes.