A response served by an inference provider carries no verifiable statement of what produced it. A recipient cannot determine which model generated a given output, nor whether the endpoint that served it was authorized by the party whose name is on it. Attribution today rests on the serving party's own account of events, offered after the fact and at its own discretion. This document specifies two mechanisms that together make that determination decidable by a recipient. The Provenance Seal is a detached signature by which a provider binds a model identifier, its own identity, and a timestamp to the exact bytes of a served response. The Serving Register is a signed document listing, for each provider, the endpoints authorized to serve its models, the public keys that validate its seals, and whether the provider declares that it seals every response. A DNS record under the provider's own domain binds that domain to its register entry and to its declared sealing policy, so that a suppressed seal is detectable rather than merely absent. The design follows electronic mail authentication: the seal is patterned on DKIM, the register on SPF, and the declared sealing policy on the published policy record of DMARC.