It's never shouted out to embarrass ...its said discretely to save embarrassment...
Do you have simular saying in your country ?
You’d subtly whisper Charlie’s dead to a woman if her petticoat was showing below the hem of her skirt, which is less of a thing than perhaps it used to be. However, the origin of the phrase, if true, is among the most gruesome ways to come up with an expression designed to prevent female embarrassment it’s possible to imagine.
Somehow, female royalists after the English Civil War thought it would be a fitting tribute to their fallen king — Charles I had just been beheaded — to dip their petticoats in his blood. Somehow this was a widespread enough practice to generate its own slang.
Conclusion: History is sometimes a very strange place.