My favorite detail on this poster is the studio name, which I have blurred out and circled in pink. What is the name? (Hint: It differs from the actual studio it's referencing in two ways, and it's a pun.)
But John isn't a common last name. You may have noticed that many of these names have two parts: Di Giovanni, Mac Seáin, and Ben Yochanan are the most obvious, but the others all have suffixes that appear in many names from the same language (e.g. many Russian names end in -ov and many Spanish names end in -ez). These suffixes all mean "of" or "son of". Thus, the corresponding English name—which is indeed the second most common last name in the U. S.—is Johnson.
Solution
As a Biblical name, John has made its way into many languages. It varies in form, but some of the sounds of "John" are (faintly) recognizable in most of the names above.
Congratulations to yesterday's solvers Jacob C., Anna K., Connor, Atticus, Leo S., Maddy, Illllllllllllllllllllia, Kate, 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 2020 to March 2021.