Have you ever glimpsed a small semicolon tattoo on someone’s wrist? While it may seem like an ordinary punctuation mark, the semicolon tattoo represents a symbolic movement far beyond basic grammar.

In April 2013, Amy Bleuel had an idea which she took to social media. It was a message for anyone who had ever struggled with a mental illness.

Sure, writers dismiss it. But the semicolon—the otherwise underwhelming punctuation mark—has had its share of fans like American physician and poet Lewis Thomas, who said the semicolon leaves “a ...