In practice provenance is an in-toto attestation with a SLSA provenance predicate, signed in CI with a short-lived Sigstore certificate tied to the workflow identity. npm shows it as a provenance badge on package pages, PyPI as attestations, GitHub through artifact attestations (gh attestation verify), and container registries store it next to images.
Provenance answers "where did this come from?", not "is this safe?": a malicious commit built by the real pipeline has valid provenance. Its value is in blocking substitution, such as a package published from a stolen token on a laptop, and in giving incident responders an exact trail. Verifiers should check the repository, the workflow path or builder ID and, where possible, the commit against expectations.