On that color card by the entry way to the ride. That looks like a standard photo calibration chart that photographers use to see how well their camera and film work. The top is a sliding grey scale that goes from white to black in a specified increment of grey called the grey scale. They use it to calibrate your TV too (if any of you have every used a calibration DVD like Home Essentials).
My bet is given its location that the rides probably have a camera system on the lower part of the ride vehicle, and that card is strategically placed to allow the camera to be recalibrated/ensure correct operation. Such a device could be used for a variety of things on a ride such as this.
Just my .02 worth.