Shady Characters author Keith Houston writes about five punctuation marks that look nothing like they used to.

The diple, which evolved into quotation marks, has the most interesting history.

The simplest was the arrowhead shape of the diple (>), or “double,” a symbol used to highlight interesting lines of text in the same way that a modern writer might underline a notable passage.

The meaning of the diple changed over the centuries. Early Christian writers, who quoted from and criticized one another’s tracts endlessly, used it to mean “here is a quote from another writer.” The diple became a kind of quotation mark, a tool for keeping one’s own interpretation of scripture insulated from the heretical falsehoods of others. By the time printing arrived in the middle of the fifteenth century, the diple was firmly entrenched as the way to call out the words of others.

Old-timers will recognize the diple as for coming full circle to become the most common Usenet quoting style before the web supplanted Usenet and quoting fell out of fashion in email clients.

The precursor to the question mark is also intriguing. 

Medieval Latin was lousy with little marks indicating abbreviations, contractions, and tone, and it seems that sentences containing a question were often closed with a kind of “lightning bolt”–the closest modern mark is the tilde (~)–that denoted a rising, questioning tone of voice.

That sounds suspiciously like what is sometimes called a Japanese wave dash, which seems to represent some sort of kawaii uptalk among younger web and chat users.