Devil Tower Star

Devil Tower Star is a message on two of the notes found on the Notes level. This note is of particular importance, because these cards are respectively 15 16 and 17 in the Tarot - which is the answer to the combination-lock in the aptly-named Tower level (151617).

One of the game ideas in the Stairs level also states "a key in one game unlocks a door in a completely separate game". This can be seen as a reference to this "Devil Tower Star" note.

1-5-1-6-1-7 is also the time it takes to create and release the games preceding the Tower level, according to Davey (read as "one game in five months; then one game in six months; then one game in seven months").

Note that the Tower is the sixteenth level in the game as well as the sixteenth Major Arcana card, so it's very unlikely that any of this is coincidental.

Devil Tower Star is also a good representative of the story overall. The Devil card represents all things evil, and we can draw this to how Davey treats Coda, with no respect for their work, pulling of Coda's work as his own. The Tower card represents major shock, which we can heavily draw to the 16th level, also named Tower, in which Coda reprimands Davey, and Davey has to come to terms with his actions and how they've hurt Coda. The Star card represents hope, and we see Davey at the end of the game wishing to change his ways and become a better person.