If angels appear on Earth and are not wearing white robes, they're probably wearing overcoats. Usually winter-weight, wool, 3/4 length overcoats. Sometimes trenchcoats. The trope frequently appears in movies where angels walk among humans, serving as a kind of Uniform Trope to communicate the wearer's angelic nature. The coats may have started as an attempt to hide the angels' wings, but the trend has stuck even in settings where angels don't have wings.