In her '70s my mother said she'd kept her mouth shut just in case she got religion in her old age but she figured she'd reached old age and still didn't believe. A couple of people in my extended family were really religious and they were viewed as a bit strange and gently humored.
There was also the practice of baptizing a child as a Catholic in case they wanted to marry a Catholic when they grew up. It was a bigger deal back then but a suitable contribution could usually get a Protestant buried next to their spouse in a Catholic cemetery or get a little excommunication overlooked.