Those of us of a certain age can remember when TV didn't broadcast 24 hours a day. After the Blue Angels had gone screaming across the sky as "The Star-Spangled Banner" played in the background, most stations put up what was known as a "test pattern." The stations kept broadcasting these cards until they resumed programming the next morning. They were also displayed when networks or local stations lost their transmission signal from remote locations. These were cards designed to help technicians calibrate broadcasting equipment as well as home TV sets.
When color came to dominate television, the test pattern was replaced by color bars, although even those are no longer needed to tune contemporary broadcasting equipment or flat screen TVs.
The most famous test pattern was one of the first - developed by RCA in 1939. It's known as "the Indian head" test pattern because of its inclusion of a Native American in full headdress.
For a time, NBC (owned by RCA) created an additional test pattern, featuring the network's biggest star: