There is no designated rank insignia for Oberfähnrich.
This is an officer-in-training rank of the Weltraumflotte.
This rank is given to those during and after the Officer's Academy if they entered directly from civilian life. If an individual is being promoted directly from warrant officer to officer ranking, they are given this rank temporarily until such time as they've proven their talents.
There are also times when a competent NCO is given the opportunity to progress into Commissioned Officer Status. This rank is given to them until they pass basic officer's training.