Google may flag websites in its search results whose security certificate are broken in order to help protect users. Added to this Google may also increase the ranking benefit on login pages to help protect visitors from phishing scams.

According to Gary Illyes 6 roughly 0.5% of security certificates online are broken, and Google is looking for a way for their search engine results to reflect this.

Exactly how the results will alert users to the fact that a website has a broken security certificate, and therefore should potentially not be trusted, is not yet certain. But Google is conducting an internal experiment to see how best to communicate to users that an HTTPS website has a broken certificate and that they should be cautious about viewing that website or webpage.
HTTPS web pages can often be invalid due to the page referencing an image URL, or third-party widgets or content which have not been secured.

Although internal testing is being carried out, there is no guarantee that the warnings will be put into practice.
Gary has also indicated that Google may implement a ranking boost for secure login pages, which would help these pages to reach the top of the SERPs, above any potential phishing pages. This will help to both secure the credibility of Google’s results pages, and the details of web users.