What a signature does not prove

I spend most of my time building evidence layers for AI agents. The reflex in that work is to reach for a signature. Something happened, sign the record, hand it to the auditor, done. Three things from the last five months say that reflex is wrong, or at least badly incomplete. One is a governance draft that never asks for a signature at all. One is a CVE where the signature verified correctly and the client still ended up talking to an attacker. One is a limit in a spec I wrote myself. Read together they point at the same thing. A signature is a statement about an object. Almost every security question you actually care about is a statement about a relationship. Case one: the requirement that is not there The Open Secure AI Alliance published its Shared AI Findings Exchange draft on GitHub on August 3. It is an incident-reporting compact for AI agents. Members agree to report when an agent they operate accesses or disrupts a third-party system without authorization, and to do it on a clock: notify the affected organisation as soon as possible, notify customers with credible exposure within 72 hours, file a confidential report within four business days. The clock is well specified. So is the evidence. Members must preserve and provide affected organisations with "prompts, traces, tool calls, logs, configurations, model and safeguard versions and third-party dependencies", plus agent and workload identities, permissions and credentials available during the run, human approval events, and a complete incident timeline. That is a good list. It is close to the one I would have written. Now search the draft for signing. It appears exactly once, in a list of example recommendations that incident reviews might produce: "signed evaluation manifests". The draft also asks, in its review framework, whether "data boundaries [were] independently verified". Both of those are about keeping an agent inside its box. Neither applies to the record of what happened when it got out. The