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The Last Signal

AI made every online social signal fakeable. Witnessed testimony is what's left.

Ken Leiserson · · 6 min read

In 2021 a well-crafted cover letter still meant something. It was evidence of care, of effort, of a candidate who could compose their own thoughts. In 2026 the same letter arrives, just as well-crafted, from a candidate whose recommenders drafted one paragraph and delegated the rest, whose portfolio is polished and may or may not be their own work. The letter, the degree, the portfolio, the recommendations: all still arrive. What no longer arrives with them is a signal.

This is not a story about AI. It is a story about verification.

The economy of expensive signals

Every institution in the modern economy runs on signals that used to be expensive to produce. A cover letter cost time. A published paper meant a peer review committee stayed up late. A licensed contractor cleared a board’s exam, in a room, with a proctor watching. A five-star review came from a real person who had actually eaten dinner. A GitHub commit meant somebody had thought carefully enough about a problem to type a solution and put their name on it. Each signal cost something, and that cost was the reason to trust it. When a signal becomes cheap to produce, it stops being a signal. The word for a signal that costs nothing is noise.

The list of signals that have collapsed in the last three years is longer than most people notice. Undergraduate essays. Coding samples for junior developer positions. Book reviews. Product reviews. Testimonials on real estate agents. The friendly outreach message that used to signal a real person had read your work. AI did not destroy any of these directly. What the AI destroyed was the cost of producing a plausible version of them, which is the same thing.

The vacuum is not new

The printing press did this once already. Before 1450 holding a book meant truth and status. Books were rare, expensive, laboriously reproduced by hand, and their content was implicitly trusted because the friction of production filtered out the frivolous. After 1550 the same book was one of ten thousand. The signal of “I have written this down” collapsed. The response was not to un-invent the press. The response was a century of confused publishers, forgeries, and pamphlet wars, and then verification. The institutions invented to fill the gap were new, but the mechanism inside them was not. The chartered societies and learned academies that emerged to vouch for a new discipline called science were guilds in everything but name: admission by the testimony of members who knew your work, standing that could not be printed, only conferred. And when the first scientific journals wanted their papers believed, they had practitioners read them first and put the society’s name behind them. We call that peer review now. It is witnesses signing.

Verification is what filled the vacuum the press created. It took a while. The Royal Society was chartered two centuries after Gutenberg. Many of the institutions we now think of as timeless were built or remade in that gap, one by one, as answers to a specific question: given that anyone can now produce a plausible book, how do we know who to listen to?

We are in that vacuum again. Not because writing has become cheap; writing became cheap generations ago. We are in it because everything that used to be evidence of care, effort, or authorship can now be produced without any of those things, in seconds, by a machine or by a person with the machine’s help. The paper, the code, the letter, the design, the review. All still arrive. None of them any longer prove that anyone in particular did the work.

Old-growth redwood forest with light filtering through the canopy.

What survives

There is one signal this doesn’t touch, and it is the oldest one: someone who was there, staking their name on what they saw.

A colleague who reviewed your code and can tell you what surprised them about the design. A collaborator who worked on the album and can name what you contributed on which track. A student who was in your lab for three years and can describe the specific patience you showed them the week they wanted to quit. This kind of testimony can be lied about, but it cannot be automated, because the thing being spent is not words. It is a reputation that took years to build, staked by a person who has something to lose if the sign-off proves false. Their reputation lives with the mark they leave on yours. That is the friction the printing press could not eliminate, and the friction the current generation of tools cannot eliminate either.

This is not a new kind of trust. It is the oldest kind. Guilds ran on it. Bar associations run on it now. Every real reference offered voluntarily, on a candidate someone actually worked with, is one instance of it. Every editor who has ever put their name on a piece by a young writer, every senior engineer who has vouched for a junior in the promotion committee, every board member who has signed off on a treasurer’s audit, is participating in an institution built on witnessed testimony.

What is new is that we have never systematically recorded it. The closest the digital era has come is the LinkedIn endorsement: a one-click vouch, offered in seconds, often for a skill the endorser never saw used. It failed exactly the way this essay would predict; a sign-off that costs nothing is noise. The best we have managed on paper, for the last three hundred years, is the letter of recommendation, which is impossible to check and hostage to the writer’s willingness to spend an hour on someone else’s career.

Recording it

The problem is recording, not trust. Trust between people who work together has always existed. What we’ve never done is record it in a form that survives, owned by the person who did the work, and shown when they choose to show it. Never pulled from a database behind their back by an employer or a recruiter or a search engine.

The vacuum the press created took a century to fill. This one will not take a century, because we already have the infrastructure to record durable sign-offs in real time, at costs that used to be impossible. The signature of a colleague, the vouch of a mentor, the certification of a professional body, the peer reviews in a journal. Each of these can now be recorded in a form that outlasts any single company and belongs to the person named in it. What is required is the collective will to record what actually matters, to protect it in ways that make it worth doing, and to keep it out of the hands of the aggregators that would immediately turn it back into another cheap signal.

The unverified signals are gone. What’s left is the signature of someone who was there.


Ken Leiserson builds tools for trust between people who work together. He can be reached at extol.work or on X @kenserson.