For life in Japan, they have gestures for "girlfriend" or "boyfriend". Girlfriend is made by extending the pinky finger. It's sometimes used in a slightly lewd way to indicate a mistress or secret lover. I've seen this gesture many times.
My wife tells me there is a similar gesture for boyfriend by extending the thumb. I've never really seen this, though I'm not a girl. I suspect it's not as common because it might be confused with "Thumbs up".