Chris performed at Summerfest with several other Idol contestants, this season, past seasons, etc. and after the show, some girl brought a sign/poster up to Chris so he could autograph it.
The security was being a bit pushy, but he did sign it, and Sway,a poster on idolforums, got a close-up picture of what he wrote.
The sign in question:
Lightened by Jess for everyone who couldn't read the original:
PS: The picture on the left, the one where they're at the keyboard, is a photochop, not a real picture.
The center and right hand side pictures are real.
PPS: If it's still impossible to read, he wrote "The Cake Shirt" Chris and a heart on the right.
He wrote Cake !!! :P and another heart over the photochop.