In most cases, certificate is signed by a trusted Certificate Authority (CA).
It can be: An SSL certificate is automatically trusted by standard Subversion clients and web-browsers if it's signed by a trusted Certificate Authority.
If a certificate is not trusted by client, the connection will be encrypted but it's not sure that client communicates with the true server.
Self-signed SSL certificate is pre-generated during the first setup of Visual SVN Server.
The main idea of HTTPS is to create a secure channel over an insecure network.
This ensures reasonable protection from eavesdroppers and man-in-the-middle attacks, provided that adequate cipher suites are used and that the server certificate is verified and trusted.
When using SVN to connect secure server, the server needs to send its certificate to the client for verification.