SignTrail is a pre-signing security control layer for digital-asset signing infrastructure. It is deployed in front of signers such as HSMs, MPC systems, custody platforms, and application or node signing services. At the moment of signing, it verifies whether a blockchain transaction request originated from a trusted execution path with its designated code, configuration, and other files unmodified. It binds the transaction payload, the request's runtime provenance, the policy context, and the signer identity into a single signed decision that is checked immediately before the signing operation executes. If the request's execution path or designated files fail verification, the signing operation is blocked and the system fails closed. Every decision is recorded as verifiable, hash-chained evidence. Unlike key-protection or transaction-screening tools, SignTrail treats runtime provenance as a required condition for signing authorization. It runs on the customer's own infrastructure and never receives or accesses private keys.