When VeriSign issues an SSL Certificate, they act as a Certificate Authority (CA). VeriSign digitally signs each certificate they issue. Each browser contains a list of CAs to be trusted. When the SSL handshake occurs, the browser verifies that the server certificate was issued by a trusted CA. If the CA is not trusted, a warning will appear.
When high-security browsers recognize an Extended Validation SSL Certificate, they sometimes display the name of the CA as well as the name of the Certificate owner.