Jesus said it. My loyalty and devotion and faith have been pledged to him. That puts me into a place of living according to the things Jesus said. Carrying that responsibility can be demanding and often time-consuming, but it's always the way we should conduct ourselves.
Now this question, "What if Christians could wear some kind of sign to designate their loyalty to Jesus, and everyone else could go without the sign, and the world would know who belonged to God and who didn't?" That would not only let everyone know we were Christians, but it would also be a reminder to us to live more like we should.
Would it surprise you to know there is a biblically based sign we really can wear? It's the real proof we are genuinely the people of God, followers of Jesus. Here's you sign. “By this all men will know that you are disciples if you have love for one another.” John 13:35
Yes, Jesus says the way the world will know I am a Christian, is by the love I have for my brothers and sisters. That's the sign you and I carry in our hearts as we show love for each other.
Can you handle more than one sign at a time? There is one more we are called on to carry, to be the proof to the world that Jesus came to us from God. John's gospel also contains this prayer of Jesus. "that all of them may be one, Father, just as you are in me and I am in you. May they also be in us so that the world may believe that you have sent me. 22 I have given them the glory that you gave me, that they may be one as we are one— 23 I in them and you in me—so that they may be brought to complete unity. Then the world will know that you sent me and have loved them even as you have loved me." John 17:21-23
This one really carries a tremendous responsibility for you and me. Sometimes I have trouble with the first sign, that of loving one another. Now comes the tender plea of Jesus for us to be in unity. Jesus tells God, "just as you and I are one, may they be one in us." That can take some work, and practice, and prayer. God didn't make everyone as lovable as me. Oh wait, sometimes I am not lovable either.
So here we are, with our imperfections and flaws, taking larger and larger steps every day to be the person God wants us to be. His word gives us our sign of loving each other as proof we are the disciples of Jesus. His word gives us our sign of being one in Him, as proof that Jesus came from God. Think of the example we can be through the church and through our individual lives if we really become God's people of love and unity.