Since there's no errata on its Arkhamdb page, I figured no one had asked this yet: if I commit Enraptured and the test succeeds, can I add a secret to my level 0 Archaic Glyphs? The wording on Enraptured doesn't seem to care if the asset has anything on it beforehand, but I vaguely remember a general rule about not putting tokens on things that don't have them already.

My guess is that I could only use it to put the second secret on, due to that general rule (and since the action triggers the third one, so that would be useless), which is a tiny bit of action economy at least. Does anyone know the real answer to this?

I'm not aware on any "general rule" you might be referring to. As far as I can tell, there is absolutely no reason why you cant use Enraptured to add to Archaic Glyphs, no matter if the card had a Secret on it before or not.

Furthermore, Enraptured doesnt specify that you have to use it to add to an asset with Uses (charges) or Uses (Secrets). You could add a Secret to a Bulletproof Vest if you really wanted to. It just wouldnt do anything. The only thing you cant do is add a Secret/Charge to something that already has another type of Use. So while it's fine to put a Charge over on Leo de Lucca, it's not fine to add a secret/charge to Flashlight, since Flashlight has Uses (Supplies).

Double-checking the rulebook, I can't find the general rule I'm talking about either; maybe it never existed and I made it up.

Your observation about the lack of any "uses (charges)" language also seems relevant, since Akachi has similar text on her, but pretty much every other card that adds tokens doesn't seem to care about what's already on the card.

So that's a great combo; commit Enraptured to put secrets on Archaic Glyphs instead of discarding it, then just put the third secret on manually and you're done in 2 actions (and you investigated successfully)!