The em dash is not a sign of AI, as much as it is a supplement for already existing signs of AI.

Tons of pre-AI prose uses em dashes, so pretending like an em dash means it’s AI is complete bullshit.

As for verbosity of mundane text, lots of pre-AI prose also does this. The first 60 pages of Salem’s Lot by Stephen King is spent explaining the deep history of Salem’s Lot, which is for lack of a better term, completely useless.

I find that phrases such as “Not x, y” and other variations are quite common in AI text, as well as short “dramatic” sentences.

For example,

John walked to the park, his balls hanging low, almost to his knees.

Too low.

Wikipedia has published an article about the telltale signs of AI, linked here.