Looking through the notebook, it doesn't take much to realize it was a detailed log of ferry arrivals. That becomes apparent when the most recent logs are analyzed, because while names are absent, each resident is described clearly enough to be obvious. "Extremely tall male. Clown? Could be strong." "Small girl. Blonde. Too young." "Giant robot. Observe further."

It seems the handwriting in the books varies. It wasn't always the same person writing the notes. And they have been writing notes on arrivals for decades, noting in the margins when resets occurred. Overall, they seem to be detailed reconnaissance notes, though who wrote them isn't mentioned. Why is also hard to track, though a detailed list of arrivals into Beacon has to be pretty useful information, right?