Just been testing site messaging on my site which is https and it’s showing the page as insecure when AC pops up a message if I either have a custom icon or put custom image in the message.
It gives me the messages:
Loading mixed (insecure) display content “http://ianbrodie.img-us3.com/admin/ian1-socmed.jpg” on a secure page
Loading mixed (insecure) display content “http://ac-image.s3.amazonaws.com/5/6/1/7/5/home/admin/ian1-socmed.jpg” on a secure page
Presumably if you load the images without the http using the //ac-image… terminology it will load correctly either the https or http version based on the http status of the current page.