"They'll remember it"

Suppose some of them did notice. The person at the next table looked up when you did the hop. Somebody clocked the jumper. The next belief is that noticing is filing, and that the person who saw the mark now has it, and that the next time they see you it'll be the first thing they think of.

Memory for strangers doesn't work like that, and the evidence for how poorly it works is odd enough to be worth telling. Daniel Levin, Daniel Simons, Bonnie Angelone and Christopher Chabris published a paper in 2002 following up an earlier finding, which was that if a stranger stops you to ask directions and then, while something briefly blocks your view, is swapped for a different stranger, a good proportion of people carry on the conversation without noticing. The 2002 paper found the same thing across several situations, and found that the people who did notice the swap were better afterwards at picking the two strangers out of a photographic line-up. In plain words, a lot of people don't hold enough of a stranger's face to notice when it's been replaced mid-sentence.

That's someone you're talking to, who has your full attention, or what passes for it. The person at the next table in the café had a fraction of that. They looked up because there was movement, they saw a person do a small hop, and their attention went back to their phone. The T-shirt observers in chapter 3 mostly couldn't say who was on the shirt when asked minutes later. What you're imagining, a stranger carrying your mark around for a week, would need a kind of memory that people don't have for people they don't know.

There's an exception, and it's real. People who know you do remember things about you, and chapter 23 covers the small town and the office where the room isn't strangers. But the ordinary public room is strangers, and the honest description of what a stranger keeps of you is nearly nothing, and what they keep of the mark is less than that.