From top left: Hermes silk twill ($165, Neiman Marcus, Mazza Gallerie); Peter Blair microprint square ($45, Sherman Pickey, 1647 Wisconsin Ave. NW; 202-333-4212); Sid Mashburn fringed Oxford cloth square in blue ($55); Sid Mashburn square in Irish linen ($25).

Once the mark of a European gentleman (or an American dandy emulating one), a pocket handkerchief was as de rigueur as a watch or hat. The 16-by-16-inch squares signified care and brought extra flair to standard suits. American guys haven’t paid much attention to this proper accessory since the JFK era. But recently, plaid or cheeky print varieties have been popping out of pockets across Washington, from the Hill to Georgetown.

“My grandfather used to say a gentleman carries two: one for the lady; one for the schnoz,” says Jason Tesauro, co-author of “The Modern Gentleman: A Guide to Essential Manners, Savvy and Vice” ($16, Ten Speed Press). “The one for the lady lives in the pocket, and the one for the nose wasn’t to be seen.”

Now, most men usually just show off the visually pleasing variety, folding squares into various shapes before sticking them into a jacket pocket.

A fresh interest in mid-century dressing revived skinny ties and fedoras. Now, the same sentiment is making the squares hip again: “It started with the revival of the ’60s ‘Mad Men’ look,” says Eric Jennings, fashion director of Saks Fifth Avenue Menswear. “But more men are also dressing business casual. Without a tie, a square gives a professional look.”

Bold and colorful silk varieties like Hermes’ silk twill are popular this fall and make a classic statement. But while psychedelic prints and wild folds work for some guys, conservative dressers should begin simply. Ethan Drath, co-owner of Sherman Pickey, (1647 Wisconsin Ave. NW; 202-333-4212) tells those unaccustomed to sartorial flourishes to begin with a white, straight-edge linen square. “It’s polished without being too adventurous or flowery.”

Whether traditional or bold, Jack O’Connor, J.Crew men’s style director, sees the square as a fresh way to salute the old-fashioned: “It’s our new favorite way to borrow style from our grandfathers,” he says. “Five years ago it was the waistcoat; three years ago, the fedora. It’s the kind of detail that shows you put in a little effort before you walked out the door.”