Google has pushed an update to Chrome that more clearly identifies pages that are loaded over HTTP instead of HTTPS.
If you'd like to prevent users from seeing "Not Secure" in the address bar in Google Chrome, you can enable a secure connection for the affected pages. This can be done by editing the page in either Composer or Page Manager.
Multiple pages (parent page and child pages) - adjust the "secure connection status" dropdown menu
Once you've set a page to load over HTTPS, you may see issues with content that was linked on that page using only HTTP. Here's a help article that explains how you can fix these mixed content errors.
At Finalsite, we're working hard to release some new tools that should assist with checking and securing pages in bulk. We'll keep you updated on our progress in our Software Update blog.