well this is one probability...and i think it also goes with both male and female this is how it goes....
when you meet each other somewhere else(example... at the park, mall, the streets...etc) and you had some conversation...then after tlaking you need to go to where your going.. then if your apart freom each other and when you look back and you saw that she or he looked back.....well I think that that person likes you.....
errr, the probable reason why she or he looked back is to have a one more glance at you....