Each time you load a page, it will show the information for each network connection and why some are secure and others aren't. The panel will indicate whether a security certificate is valid and if you're using the proper connection protocol. It also flags the dreaded "mixed content" issue that arises from insecure HTTP subresources. From there, you can drill down to see which resource, exactly, is borking your page's lock.

To use the new panel, developers just need to open up the Chrome 48 dev tools, or click on the URL lock icon and select "details." The new version of Chrome also brings a number of bug fixes and eliminates the old and insecure RC4 encryption scheme. The stable version started rolling out yesterday and should hit most regions soon.