At the start of the Dark Story when Dr. Eggman releases Shadow, a message can be seen on the edge of the pit where Shadow was held that reads:

"ASTRONOMERS ARE CONCLUDING THAT MONSTROUSBLACKS"


This message could be an early or unrealized hint at the existence of the Black Arms, the antagonists of the spin-off game Shadow the Hedgehog, or something similar that went unused in Sonic Adventure 2.
Contributed by MehDeletingLater
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