Yes, this shirt actually exists. From the product page:
We’ve applied Cybertronian Hydrophobic invisible ink in the shape of an Autobot logo. But much like the Transformers, you’ll need an alt mode to fully experience this Transformers tee. Simply put, you need to get this shirt wet to see the Autobot symbol. Get there however you like. Maybe you want to earn it in the gym or on a hike. Maybe you want to surprise your friends after a rousing water balloon battle. It’s up to you how you want to surprise the world with your amazing new Autobots shirt.
Or maybe you’re just a really sweaty Transfomer. Transform and roll on some deodorant!
Product Page ($35)