The "Kansas Under 2M" tags that you see are not issued by the state, they are purchased at RV and Boat stores in the state if Kansas. Trailers under 2000lbs in Kansas are not required to be registered, that is true. These tags just fill the spot for the license plate.

I think you might have trouble explaining to a police officer why you have an exempt trailer in Kansas without a Kansas driver's license or a Kansas tag on your car.