So, younger readers, certain older displays were way more susceptible than today's TVs for something called burn-in. That's when parts of an image would stay on a screen for so long that they'd literally burn into it, creating a permanent "shadow".
Think TV network watermarks, or the margins of a news ticker. You'd normally see it on TVs that were always on, and always on the same channel. Like those in bars, or airports.
You could also see it on CRT arcade screens. The older the game, more more beautiful the burn-in.
Video game screen burn in [Reddit]