The picture above is not that of the specialisation of a Royal Navy Communications Yeoman, i.e. Tactical; instead, the badge shown (aka Flying Ball of Sh*te) is the branch badge of the General Communicator in which the CY's counterpart is known as RS; this apparently stands for Radio Supervisor but in certain cases can also designate either Rarely Seen or Rarely Sober.
In the good old days of paper tape and hard copy signals, the rest of the wardroom made do with using the Officer's Reading File in the MCO, but the Skipper would have a personalised board on which would be clipped his signals. To distinguish these signals from those of other readers, the Skipper's signals would have been specially coloured in by the Yeoman, leading to his designation as "Flag Officer Highlighters".
Apparently described as An Assistant to a Command office.