Jesus in John 17:18 says, "As You have sent Me into the world, I also have sent them into the world." Those are pretty powerful words. Powerful enough to make you stop for a second and think about the implications of that prayer by our Lord and Savior to the Father.
Christians are a "sent" people. We were never intended to be a "went" people. We are, in fact, a "sent" people. "Went" people dilly-dally in their own gumption, their own initiative, and their own humanistic will power. After they've "went" they feel good about themselves, thinking, "Yeah, I think I did God a favor there. He owes me for this one." "Sent" people are empowered by the command of Jesus and the presence of the Holy Spirit. Christians are Spirit led; Christians are "sent". The important thing about being "sent" is that it is always present tense. It is "go", it is "now", and it is not doing God any favors, but simply being about the Father's business in love.
Knowing that Christians are "sent", why not wear a t-shirt that is a reminder of the calling? Wearing it might even force the issue of being "sent" simply because it begs for questions by those you encounter. A shirt can begin conversation and if it can begin conversation, then you truly are well on your way to living life "sent". Gregg always likes to say, "What you believe in your heart, you confess with your t-shirt." Perhaps the very confession on your shirt can serve double duty, as a reminder of a "sent" calling in life and also open the door for a conversation about Jesus.