My setting involves a masquerade (though in this setting the term used is "The Veil of Ignorance") where numerous immortal humanoid beings live in secret amongst humanity as a 1-in-1000 minority. There is an independent immortal organization, known as the Veilkeepers, tasked with keeping humans from finding out about immortals, and with punishing those who endanger this secrecy.
Initially I thought this would mean that immortals would not have writing, photos, or any other sorts of physical documentation, as a lot of that would be catastrophic if it leaked, and forgetting where you put just one single photo of a blatantly-non-human friend, or maybe even just one incredibly suspect handwritten note, could have disastrous consequences for the Veil.
I recently came up with an interesting solution: There's a symbol the veilkeepers came up with, and they have used their memory-manipulating powers to program the entire human race to be absolutely incapable of finding anything marked or watermarked with the symbol to be even slightly interesting or worth their time.
The problem is that I swiftly realized that unless I make up some justifications for why you can't do certain things with this symbol, it is very decidedly a nuclear option that will kill a lot of potential sources of conflict and make it far too easy for certain villainous immortal groups to prey on humanity unhindered:
What exactly is stopping someone from taking a bedsheet, putting this "ignore this" symbol all over it, and then using it as an invisibility cloak, rendering humans incapable of noticing whoever is wearing it?
If I can't produce a compelling answer to this question, then not only does that kill a lot of potential plotlines about the difficulties of being a non-passing immortal species trying to live among humans, but it also means that humans would be 100% defenseless against any immortal who would try to do them harm.