Signed Certificate is a Digital Certificate that is verified and issued by a trusted source.
Signed certificate confirms to your browser that this server information has been verified by a trusted source - the domain name is legitimate and a valid certificate has been issued.
Web browsers check that an HTTPS connection is signed by a recognized CA. If the connection is self-signed it will be flagged as risky and browser will try to prevent user from visiting the site.
In typical public key infrastructure (PKI) arrangements, a digital signature from a CA attests that a particular public key certificate is valid. Users, or their software on their behalf, check that the private key used to sign some certificate matches the public key in the CA's certificate.