The answer is real simple. Educate the girls in literary works like the Bible. very often, the word “man” or “men” very often refers to the general population of (hu)man, the human race. What the sign meant is (Hu)Men Working. Sure, there might be (Wo)men there also, but in the general sense, they are mankind, of the human race. Currently prevalently masculine beings, yes, but all are “Men.”
I thought they were womxn now.