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 represents peace and good fortune, and was also used widely by (i)ndigenous people worldwide in a similar vein. But in the West, this symbol is often equated to Adolf...