Thirty-six years ago, when Bilal Egilmez opened his shop, Genius Tailor, in the Lenox Hill area of Manhattan, colleagues wished him well but warned that no one would come to a basement business accessible only through a seven-step metallic stairwell under the stoop.

“Henry Ford worked in a basement,” he said recently, recalling his response to naysayers. “And so did da Vinci in the 1400s. Why shouldn’t I?”

To ensure that customers could find his store, stashed on a residential and commercial tree-lined block at 65th Street and First Avenue, Mr. Egilmez designed two large green and white canvas banners. One hangs vertically on poles along the building’s facade, while another is displayed over the entrance.