This is pure speculation and has no basis in the case: Unibomber was a very smart guy. Math PhD. He was cryptic and went to great lengths to stay hidden He alluded the police for a decade plus. Numerous psych profiles were totally wrong. He was untraceable. His bombs were built from used scrap parts or simple manufactured parts. No tractability to point of purchase.

Here is my speculation.
They might have been looking for keys coded writing. Having the cabin intact to the nail would allow them to go back and look for the keys to read codes. A good key wouldn't be too hidden, it would be accessible and have a dual purpose. Book cyfer, I'd say a solar sun dial but that would be so complicated. Again the guy was a literal genus.

Game recognise game.