Someone on the DT subreddit found this photo here:
https://www.gettyimages.fi/detail/photo/real-human-skull-profile-royalty-free-image/96370388Which proves that the "137" was intentionally placed, rather than a marking that was already on the skull.
Some have already said that if you count 6DOIT as one song, and ITPOE as one song, and include ACOS, that's exactly 137 songs from all their released albums plus the only original song on the EP.
This to me means that the skull symbolizes the past, the android holding the skull is their present.
This album is about the fact that their past, symbolized by the skull, is dead. The new album is The Android, and it represents a new chapter in their lives (InsideOut records rather than Roadrunner and everything before it).
The android is holding the skull to acknowledge that even though the past is dead, they still put it on display as a form of respect. This coincides with their statements that the I&W tour was a huge inspiration, and also the fact that the DOT tour is going to celebrate SFAM.
And one final tidbit is the lyrics from the teaser: "Don't be afraid of letting go [of the past]. Open your heart, be set free"