How do I fix mixed content warnings preventing my secure green lock icon from showing?

Mixed content defects manifest when a site with an active SSL certificate attempts to source assets, script hooks, or styles using old unencrypted HTTP link structures instead of secure HTTPS pathways.

“This is usually a handful of assets still calling old HTTP links even though your site has SSL active. I’ll clean those up and get your lock icon back within 24 hours for $99.”
— Jeff Bollettino, Managing Director, Ignite Conversions