People like people who are interested in them. I was lunching with a girlfriend recently. She spent the rest of the lunchtime doing everything she could NOT to look at him. How are people going to know you are interested if you don't show them. There are millions of people out there who are just like my friend.
Someone has to make the first move.
If you are interested in someone, smile at them . It's not an invitation to engage in sex, it's just a nice way of shining your light. Recently I have started wearing Indian Bindis on my forehead. I get stopped in the street by all kinds of people asking what it is, how it sticks on etc. I have given people a reason to talk to me.