An em dash surrounded by spaces on either side tells you it was AI.

AI: This is how we think about these things — because they're important to think about — when we want to accomplish a task.

More likely human: This is how we think about these things—because they're important to think about—when we want to accomplish a task.

Not bulletproof for obvious reasons but it's easy to spot who was at least lazy with AI using this heuristic.

No, this is American style (long dash without spaces—like this) vs. European style (middle dash with spaces – like this).

I don't think it is useful to detect AI writing. I told my AI not to use em dashes.

I mean, no. When I em-dash -- or double-hyphen -- I always surround it with spaces; seems wrong not to.

Spaces around em-dashes are a convention which changes depending on the style guide.

The most telling sign is when they don’t make sense — for example right here.

A human puts em dashes to emphasize the break in thought or rhythm. Where there is already a break in thought or rhythm a human would just write a comma or nothing.

Another tell is what is inside the em dash. It often doesn’t logically follow – like an ad on a radio show.