Originally Posted by taxlady
"be like Dad and keep Mum"
Never heard that one before. I love it and will try to remember it.
It was on a famous and much quoted British WWII poster warning people that "Careless talk costs lives". If you Google it you can see a selection of the posters including the one with the glamorous blonde with a sailor, an airman and a soldier oggling her and the caption "Keep mum, she's not so dumb"
I think in USA they had a "Loose Lips Sink Ships" campaign among others.
(I was a product of the post war baby boom and these sayings were still very common in my childhood.)