The OP said that they kept what they liked and discarded the rest. I think that's a reasonable definition for signal; so, the signal-to-token ratio would be a simple ratio of (tokens committed)/(tokens purchased). You could argue that any tokens spent exploring options or refining things could be signal and I would agree, but that's harder to measure after the fact. We could give them a flat 10x multiplier to capture this part if you want.

I'm going to call it out as bullshit, you can't dig out "what you like" from "hundreds agents running all the time".