There’s a look
The stereotypical look of the Karen means that it’s pretty easy to spot them in the wild. You can check the hair, the folded arms, the hoop earrings off of your list. It is also pretty easy to spot them by the way they’re standing by the counter of the establishment you’ve entered looking like they’re about to complain about something.
The meme poster here is pretty confident that she’s found a Karen and knows exactly what is about to happen. I think they’re probably right, and if I were them I would be backing out of that place ever so quickly. Otherwise, they’ll find themselves in the middle of a hissy fit of epic proportions.