Google Chrome is the first browser to implement support for the Certificate Transparency Log Policy. Starting today, Chrome will show a full-page warning whenever users are accessing an HTTPS website that’s using an SSL certificate that has not been logged in a public Certificate Transparency log. The new policy was first proposed by Google engineers in 2016, and was scheduled to enter into effect in October 2017, but was later delayed for 2018. Other browser makers have also agreed to support this mechanism in the future, albeit they have not provided more details.
Source: https://www.bleepingcomputer.com/news/security/starting-today-google-chrome-will-show-warnings-for-non-logged-ssl-certificates/