Enlisted have ratings, such as YN for Yeoman, QM for Quarter Master (not at all like an Army Quarter Master), OS for Operations Specialist, etc. An E6 who is a YN would be a YN1. If a person with a rating has a further specialty, that would be an NEC, Navy Enlisted Classification, for things such as being an Air Traffic Controller or Navy Rescue Swimmer.
Officers have designators. For example, I was an Unrestricted Line officer in the Surface Warfare Community, so I was an 1110. Then we have qualifications. For example, Surface Warfare Officer being the main one to actually be an 1110, but I was also Engineering qualified, Tactical Action Officer, Combat Information Watch Officer, Command qualified and several others.