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.