What does the cross tattoo on the index finger mean?

well, if your catholic then you know that when you got into a church you put your index finger in wholly water and you tap your forehead the middle of your chest then your right shoulder then your left. some people kiss that finger after words but it inst required. when you tap your forehead its the father, middle of your chest the son , both sides make the wholly spirit and when you kiss your finger your saying amen. that might be a little over helpful but there you go.