It seems to be a hipster trend in the Bay Area. At least, the only people I know that do it are hipsters and don't do it for religious reasons. However, this

It seems to be a hipster trend in the Bay Area. At least, the only people I know that do it are hipsters and don't do it for religious reasons. However, this is the Bay Area, so it might not have any relation to why people do it in Iowa, say.