Listen up, kids, this is how it worked: When an admirer decided to write to you, they’d take a sheet of paper, inscribe deep thoughts upon it, and mail it. A few days later, an envelope with your name on it would appear in the mailbox, like a gold nugget in a sandy stream bed, among your parents’ ultra-boring mail. The convention was to reply, in order to encourage or deflate. Either way, the letter, now yours, could be saved, shared, dramatically burned, or indifferently tossed. That was how to slide into someone’s DMs, 1980s style. And 1660s style? Go see “Vermeer’s Love Letters,” now at The Frick. Mounted to celebrate the renovated building’s reopening, this micro-exhibition displays three of Vermeer’s six paintings that depict women with letters. Looking at the three paintings together, it’s apparent why the exhibition designers chose to offset the displays from one another: to discourage viewers from bringing strings and pins to create their own crazy walls, tying together share...