Of course, the best place to start is with the official source. On AHS's official Twitter, they dropped a promotional tweet to tease this year's Comic-Con exhibition. The AR (Augmented Reality) experience will allegedly reveal "terrifying mysteries" that are "hiding in plain sight." Here's the thing with Augmented Reality: whatever special hardware or technology they're using, it will have to interact with the environment that's already there. This is probably what they mean by "hiding in plain sight" — the experience will layer hints onto the objects in the room.
I mean, you can also read this whole "hiding in plain sight thing" a lot more literally. As in, there are literal clues for season eight strewn around the exhibition. Which brings us to the less concrete pieces of evidence the internet has unearthed so far.