Gigi Hadid’s 30th birthday celebration was a stylish reminder that sometimes it’s the smallest details that say the most. At her dinner at L’Avenue at Saks Fifth Avenue in New York City on Friday night, the model kept things sleek in a white corset top, black leather pants, and slingback heels. But it was her jewelry that had people looking twice — specifically, a black-and-white checkered ring sitting squarely on her left ring finger.