While the fashion world is often drawn to new and shiny hot spots like Omar's or Acme, it's Omen, a dark, unassuming-looking Japanese restaurant on a sleepy block in SoHo, that has served as the unspoken clubhouse of the city's stylish sets since the early "80s. And with the international fashion community descending on New York in the next few weeks, Omen (which recently changed its name to Omen A Zen) will be in full swing. At first glance, it's difficult to see why big names flock there. Even the owner, Mikio Shinagawa, is mystified. "Why Omen?" he asks. I would like to know why Omen is so charming. But it's precisely the haunt's un-chicness - the homey décor, the menu of health-focused Kyoto cuisine that harks back to the days before the latest culinary revolution, the feeling of being a last vestige of SoHo's reign as a nucleus of the city's creative scene - that has made it "an industry canteen," as the creative director Doug Lloyd puts it. It's a place where familiar faces - Patti Smith, Karl Lagerfeld, Rem Koolhaas, Terry Richardson - can blend into the background. "You will know everybody at each table, but you don't feel you have to talk to them," the artist Anh Duong says. Derek Lam calls it "a place to decompress." Indeed, the restaurant seems barely affected by its starry clientele. Reservations are not hard to come by, and a famous regular might simply get a nod from the owner. "They don't welcome you like you are their best guest," Franca Sozzani, editor in chief of Italian Vogue, says. "It's like, "What's your name? O. K., you go sit over there." " Omen A Zen, 113 Thompson Street, (212) 925-8923.