Yeah, you can thank web browsers for trying to force all sites to have https full-time. Nothing has changed with the site in this regard, but since it's a normal http connection, browsers are displaying "Not Secure" to scare people. The login forums do use https, and as PlayWithWolves noted above, the store forces https full-time. However, this version of the forum software does not support https (outside of the login forms) and there's nothing I can do about that until I upgrade the forum.
Once I get past the holiday crush of orders, my absolute number one priority is to get the forums upgraded. I have to finish some work I've been doing on the main site first, which is a prerequisite for updating the forum. It'll probably be a good month's worth of work full-time between the site and the forum to do this. Once those are finished, I also plan on moving the store to completely new (and much nicer) software. Everything will be on https by default when I am done.
The forum does present some unique challenges as far as https goes. Since users can link to off-site content (like images), to properly maintain 100% https connectivity, you need to cache any linked images or content. The new forum does support that, but it is more work to setup and may require additional costs if this content is hosted by a third-party. It's not something I've played around with yet. I am running the new forum software on another forum I run and it's quite nice compared to this version. They rewrote the entire thing from scratch.