It says Mommy and Niko. He told me that it meant that Mommy can come into Niko's room anytime. He said that Daddy is welcome too, but the sign was so I would know that I can come in his room whenever I want to.
I took a TON of photos with him posing in front of the sign.... so in a few years, I can show him that that he once wanted me in his bedroom!
(BTW... every now and again, I take a photo of Niko that reminds me of my brother... the bottom photo totally reminds me of Donnie as a kid.)