Hindus, Buddhists and Native Americans are trying to rehabilitate the swastika, a symbol of peace and prosperity, and to restore it to a place of faith. NEW YORK — Sheetal Deo was shocked when she got a letter from her Queens apartment building’s co-op board calling her Diwali decoration “offensive” and demanding she take it down. “My decoration said ‘Happy Diwali’ and had a swastika on it,” said Deo, a physician, who was celebrating the Hindu festival of lights. The equilateral cross with its legs bent at right angles is a millennia-old sacred symbol in Hinduism, Buddhism and Jainism that...