The symbols above the numbers on a QWERTY keyboard are !@#$%^&*().
What's the common connection?
You might not have heard of the Japanese kappa, but I bet you've seen kappa (cucumber) rolls on a sushi menu. Note what favorite food the kappa in the picture is munching on.
Solution
The connection is Greek letters (Delta Airlines, Catherine Zeta-Jones, kappa, chi-square distribution, Omega Watch).
Congratulations to yesterday's solvers Maddy, Jacob C., the Greggs, Kate, Dr. Yetman, and Graham. Thanks to everybody who made a guess!
Ten years later, Dr. Shapiro revived Puzzle of the Day at Proof School, writing each day's puzzle on a name tag. After 600 puzzles or so, he was just starting to feel normal about students reading his chest all the time when campus closed and the puzzle, like the rest of our lives, moved online. New puzzles are posted daily on school days.
Want to catch up on old PotDs? There's an archive currently containing puzzles from March to December 2020.