On the vast Midnighters spoiler comment thread, someone was asking what a tridecagram (a 13-pointed darkling-slaying star) looked like. So I was poking around on Google and discovered this:
That’s a thirteen-pointed crop circle! That’s right, even aliens are into darkling protection. (Aliens with lots of spare time, anyway.)
Here are some more crop circles, including the one above. They’re really quite beautiful. And frankly, they’re a lot cooler if mischevious humans make them by stomping around with compasses than if aliens whip them into existence with their stalk-cracking ion drives.
Or maybe midnighters make them, under the strict instructions of polymaths.
That would explain why they just appear in the middle of the night, after all.