Overview#SignatureValue is a Basic Certificate Field defined in RFC 5280 section 126.96.36.199 contains a digital signature computed upon the ASN.1 DER encoded TBSCertificate.
The ASN.1 DER encoded TBSCertificate is used as the input to the SignatureAlgorithm function. This signature value is encoded as a BIT STRING and included in the signature field. The details of this process are specified for each of the algorithms listed in RFC 3279, RFC 4055, and RFC 4491.
By generating this signature, a CA certifies the validity of the information in the TBSCertificate field. In particular, the CA certifies the binding between the Public Key material and the Certificate Subject of the certificate.