To sum it up, it really depends on where you're located and the codes HR is using. I work for the State of Illinois and my title is a Forensic RN2 which means, I'm a Nurse Supervisor and my department I work in.
RN is just starting; RN1 skilled nurse with some years under their belt; RN2 = Nurse Supervisor; RN3 = ADON & RN4 = DON.