it's hard to speak definitively but some telltale signs are 1) lots of random single-sentence paragraphs especially at the beginning of scenes 2) overuse and MISUSE of em dashes. can't stress this enough bc i love em dashes ai just doesn't know how to use them. 3) ai really likes to repeat phrases for some reason... other than that idk how to explain it but if you're someone who writes often you can usually just Tell when a robot wrote smth