It’s hard to believe now, but television didn’t used to be a 24/7/365 affair. TV stations stopped broadcasting late at night and when they were off the air, they would commonly display a test pattern until programming resumed in the morning.

Used since the earliest TV broadcasts, test cards were originally physical cards at which a television camera was pointed, and such cards are still often used for calibration, alignment, and matching of cameras and camcorders.

From Wikimedia Commons and Present & Correct, here are some vintage test patterns:

Vintage TV Test Patterns