Blue stop signs exist but aren’t issued by the U.S. Department of Transportation. They’re typically found on private property like gated communities, parking lots, or campuses, functioning without legal enforcement. In the 1910s, stop signs were yellow with black lettering. By the 1950s,
red became the standard due to its strong association with warnings. Traffic sign colors have specific meanings: blue indicates services, green gives directions, yellow warns of hazards, and black-and-white signs,