Cupid's bow 
noun
A shape like that of the double-curved bow often shown carried by Cupid, especially at the top edge of a person’s upper lip: [as modifier]: soulful eyes and Cupid’s bow lips...
- Here is a podgy youth seen face-on, the emphasis being on the Cupid's bow of his all-too-feminine lips.
- There is a collapsed viola, pegs extending beyond the apron of the sculpture's black-and-white-tiled stage, and a Cupid's bow and arrow that hang from the wall above the angular presence of a scaled-down chair.
- She has this fat, squishy section on her bottom lip, like an upside-down Cupid's bow that just begs to be kissed.