why can't the current King of France be bald or bold? It is not true but what is unlogic about it?

Well, in logic the sentence is neither true nor false, because there is no referent for "the current King of France". You can read up on it in this Wikipedia article. I also see that I misremembered Russell's example sentence; it is "the present King of France is bald". (Also, I think that Russell was making a teasing reference to an actual, but deceased, King of France, i.e., Charles II le Chauve (in English "Charles II the Bald"). He is not to be confused with Charles le Hardi or le Téméraire, duc de Bourgogne (Karel le Stoute in Dutch, Charles the Bold in English).

Ceci n'est pas un seing.