A relatively simple but damaging signature . Looking at the two elements, the effect and the discard condition, we get:
The effect: The sharp needle in Joe's Insight haystack, this is going to cost you an action, 2 resources, and maybe a clue. Note that you can play it even if you don't have a clue, which makes it considerably less damaging. Joe needs to keep 2 resources on hand until this gets drawn, and it could cause an AoO if he is engaged when it comes up, but, despite the nasty effect if it fires, this is not a terrible threat. There is no particular mitigation, beyond making sure you have those resources or a quick way to get them. If Joe has somehow managed to translate the Cryptic Grimoire, he can play this fast. That Tome would generally help Joe, even if it's not hugely feasible for him to translate it without a cooperative Rogue or a lucky draw of the Dread Curse Weakness during deck building. Farsight could also help, but it's got a high opportunity cost for Joe. Other than that, there aren't a lot of card interactions. You can't even troll your party by playing Eidetic Memory, since Unsolved Case is removed from the game.
The discard condition: Another "one and done" Weakness, and one that removes itself from the game after playing, so it won't recur, even if Joe decks himself.
Summing up the facts, this is a way below average signature Weakness, in competition to be the easiest in the game.