Most of my shirts were similar. They were bold, quickly evangelistic, and perhaps a bit offensive. They employed a billboard effect and used simple messages.
“Be cool. Meet Jesus,” said the front of one. “Or fry in hell,” on the back.
Going further back, there was another fashion trend that was popularized among the kids in vacation bible school. They were little bracelets with five colored beads which were reminders of the basic truths of the gospel. We called them power bands.
Their purpose was mostly to serve as evangelistic tools. To that end, the bands were probably better than the T-shirts. There are more poorly conceived Christian t-shirts in the world than effective ones.
Still, there is something deeply scriptural about wearing clothing items that point to Jesus. Consider the command in Deuteronomy 6.
Listen, Israel: The LORD is our God. The LORD is the only God. Love the LORD your God with all your heart, with all your soul, and with all your strength. Take to heart these words that I give you today. Repeat them to your children. Talk about them when you're at home or away, when you lie down or get up. Write them down, and tie them around your wrist, and wear them as headbands as a reminder. Write them on the doorframes of your houses and on your gates.
The Biblical purpose is not so much to be a walking gospel billboard (Eat at Joe’s), but to create a daily reminder of our identity, both for ourselves and for others to see. We become targets for both seekers and antagonists. We also remind ourselves moment by moment the necessity of dying to self and living for Jesus.
One more thought. There are some who wear religious items, carry rosaries, or even get religious symbols tattooed on their skin, but neither as a commercial nor a personal reminder. They hope that by doing so, they will receive some mystical power or spiritual blessing or protection. There is nothing biblical about that at all.