This is value on the imgsec:Key record, holding the actual key material (or a fingerprint referencing it) for this specific trusted signing key recognized by the image-security policy. An admin verifying that a firmware bundle's signature was checked against the expected key compares this value's fingerprint to Cisco's published key fingerprints, since a mismatched or unexpected value here would mean the wrong key is trusted. In practice this looks like a long hex-encoded string or certificate blob unique to that one key, not a human-readable name.