Hi Paul,
This is my interpretation: It means that the Notary Public who, I suspect is part of the staff at the embassy, has been approved by the FCO and/or the IDFA to carry out such work. Of course, I may be wrong.
It is worth noting that a signature from a common or garden Solicitor is NOT the same and would not be acceptable. Some Solicitors are also Notary Publics but most are not. My recent Visa application had to be verified by either a Solicitor or Notary Public. My Solicitor charged me £5 to sign 2 documents but, had I gone to my local Notary Public, it would have been closer to £150. Those guys are not shy at charging top whack.