The winky face is used to imply to the opposite sex (or same if you sway that way),
that your keen as a bean for their Dick or Vagina!
Jess: Chris asked me if I was free tonight
Chloe: did he put any emoticons?
Jess: Yeh he put a winky face at the end of the sentence
Chloe: HE WANT'S YOUR VAGINA!!