How do site visitors know if a web site is using SSL?

When a browser connects to a secure site it retrieves the websites SSL certificate and checks that it has not expired, that it has been issued by a Certificate Authority the browser trusts and that it is being used by the web site for which it has been issued.

If it fails on any one of these checks the browser will display a warning to the end user. If it succeeds, several security indicators are built into modern browsers to indicate that SSL is enabled.

The beginning of the URL or web address changes from http:// to https:// and a padlock on the browser window changes from open to closed.

In modern browsers, the address bar will turn green and display the name of the web site owner when connecting to a web site protected by an Extended Validation SSL certificate. A trust mark such as the RapidSSL site seal may be added to web pages on a secure site.