Thin red line flags: Understanding the origin, meaning and controversy
Thin Red Lines & Blue Lines: The Meaning and Paying Tribute | QALO
Architectural Redlines | Life of an Architect
What does this US flag with a single red line mean (the placement of the redline doesn't really match with the firefigther one that's why I'm asking) : r/Symbology
The Red Lines In Your Business and Life – ISR University