When it was WKBG, Channel 56 used to play "That Happy Feeling" over the test pattern and during station IDs during regular programming. As to why, who knows? Maybe because no actual testing was going on during those test pattern transmissions, so it didn't matter what audio accompanied the slide. It certainly made the station stand out, at least to the geeky kids like me who'd get up really early to check out test patterns and sign-ons.