I don't know how it started but my boyfriend and I have a secret way to say I love you to each other. This is great for when we are around others and want to notice each other.

He'll come up to me and scratch my ear. This is his way of telling me in a room full of people he loves me.  It has since evolved and the other person will scratch their nose to return the gesture. It is a great way for us to have  a special language to say I love you that no one else knows without the PDA (public display of affection).