Both Firkin's and Stephen's interpretations make sense. My own view is that readers eventually arrive at Stephen's interpretation (or something very like it) only after a complicated emotional journey.
It goes like this:
Readers look at panel 1 and then at panel 2 and understand them to be saying single women show lots of cleavage cos they want to attract sexual partners but married women don't show lots of cleavage as they don't want to attract sexual partners.
They think they've understood the first two panels but then they come to panel 3 and it's clearly saying happily married women don't show any cleavage as they don't want to attract sexual partners.
Confusion sets in, because panels 2 and 3 are very different and therefore can't be saying the same thing - so what is panel 2 actually saying?
Then it hits them. They realise panel 2 is saying married women who show any cleavage at all are looking for sexual partners.
At that point, all cleavage-displaying wives are shocked. The faithful ones question their inner desires and the unfaithful ones are horrified to learn that their (relatively modest) cleavage display is actually a confession of adultery for all the world to see.
And what about the husbands of cleavage-displaying wives? What will they be thinking?
