I've always loved the quote going to church on Sundays doesn't make you any more a Christian, than standing in the garage makes you a car.
When people are God centred, their actions, words, indeed their whole life is a testimony to the path that they're following. John 17:3 indicates their focus, and often these ones are known solely by the fruitage of the spirit; namely peace, goodness, faith, joy, happiness to name a few. They are also known by their love for one another.
We know that the two greatest commandments of all, are to love God with your whole heart, whole soul, and whole mind, and the second to love your neighbour as yourself.
The first one may be easy when you're God centred, but the second one poses some serious challenges at times as people are prone to make mistakes, and more often than not hurt you. To love those ones as yourself, now that's what makes one a true Christian.
To that end, this is the type of person I try to be. Sometimes I succeed, sometimes I fail, but I keep trying because I know it's the best way of life, and it leads to the greatest of joy.
Be leery of who claims to be Christian online. I have had many men online change their minds as to what they are just to agree with me after we start some personal communication. If they have denied Christ in their profiles and then proceed to tell me they're Christian, i want absolutely nothing to do with them. They lie about their belief in Christ (or hidden their belief to appeal to more people) then what else do they lie about? I do NOT what to know!!
Being a Christian or Catholic is a way of life for me. God is the reason why I exist and keep on existing. He gives me wisdom to make the best decision in every situation and He's always there whenever I need Him.