With the app Hiddenhint you simply add someone you are interested in to your secret list. He or she will then receive an anonymous message explaining that someone is interested. If the person you are interested in adds you, a match is made. You now know that you are both interested in each other and can take your relationship to the next level.
OS 1.5 - 2.3.3
Link to this app: http://thebetafamily.com/social-networking/hiddenhint-android