It says "fake psychic. real detectives." with a fist bump underneath. It's a reference to a TV show called "Psych." I couldn't find the exact t-shirt he's wearing, and the only "official" listing I could find is in the NBC Store (I can provide a link if you want, but t-shirt links on social media always look a bit fishy, so I won't include one in this reply; you can also just go to the NBC Store and search for "fist bump" there).