An RN code is a type of personal code, given to mentally challenged people and criminals.
RN code

A diagram showing how the RN code works. The RN code featured in this image is Homer's RN code.

Each mentally challenged or criminal citizen of Tyksrr has a personal RN code. 

How it worksEdit

The first number of the RN code is "the severity of the mental retardation", on a scale of 1 to 10. The next number "refers to whether or not the criminal was born retarded or became it in later life" (1=Born, 2=Later life). The 3rd number refers to the sex of the criminal (0=Female, 1=Male). The last number is "the number assigned to differentiate the criminal from other criminals".