As you ride Monsters Inc at Disney’s California Adventure pay attention to the control panel toward the end of the ride.

There will be all sorts of buttons, levers, and switches.  Towards the center of the control panel you will see a turn dial and two circular gadgets above it that form a classic Hidden Mickey.

Below is a picture of the control panel on the Monsters Inc ride with the hidden mickey.

Inside the building of the Monsters Inc ride at Disney’s California Adventure there is a poster on the wall that says "Monstropolis" with a picture of a yellow cab. 

If you look at the headlights of the cab you will notice a classic upside-down hidden mickey.

Below is a picture of the Monsters Inc hidden mickey.