Like fashion trends, fads in book covers come and go. One year, the backs of women’s heads might be all the rage; the next, soft focus photography. And who can forget the exploding flower craze? Or the proliferation of flames on jackets, from thrillers to science fiction to self-help? But the look that’s commanding today’s runways — a.k.a. bookshelves — is not so incendiary. It tends to lay blaringly bright type in a sans-serif font atop a painting, usually a few centuries old but not always. Facial expressions are baleful or dyspeptic; an aggressive burst of spray paint can change the tone entirely. These covers are the new signifiers of stylish literary fiction, telegraphing gravitas, wit and cool. They make a bid for a certain kind of reader — more city than suburb, more pét-nat than chardonnay. They wouldn’t be caught dead alongside a volume decked out in pop art or, god forbid, metallic lettering. Thomas Haggerty, a senior account manager at Bridgeman Images, which licenses paintings for commercial projects, credits the trend to “the power of juxtaposition.” Gregg Kulick, executive art director at Hachette Book Group, agrees: “Poppy type” reads as fun, he says, while the paintings “hint at the academic.”