What do the two bitter moles on the back of the neck mean?

According to the Ming Dynasty's "Old Guo Hangzong":

The bitter nevus is located in the center of the back of the neck within 1 inch (about 3 cm in an inch), which is a very auspicious omen. People with bitter moles, although love is hard and difficult, will be sweet and stable after getting love, and there will be no marriage change. According to the grapevine, the mole is located in Kun.