Most "audit logs" ask you to trust the company that keeps them. Signet's seal is different: it's a piece of cryptography that anyone can check independently.
Your browser recomputes the document's fingerprint and tests the seal against Signet's known public key. If either the document or the certificate had been tampered with, the check fails. Nothing is uploaded, and it works even if Signet is offline. So the proof stands on its own maths, not on our reputation.