Both WordPress URL and site URL can start with either %1$s or %2$s. A URL starting with %2$s requires an SSL certificate, so be sure that you have one before changing to %2$s. With %2$s, a padlock will appear next to the address in the browser address bar. Both %2$s and the padlock signal that your site meets some basic security requirements, which can build trust with your visitors and with search engines.