I looked at the Brunei signatures and it seems like Brunei have got two issuing entities, according to SCWPM, Banknote museum and what's written on the notes:
Kerajaan Brunei: Goverment of Brunei
Example: N#218110
P#1 - P#12
And
Negara Brunei Darussalam: The country of Brunei Darussalam
Example: N#210873
P#13-date
Alternatively:
Central Bank of Brunei, which either opened in 1967 or 2011..?
https://en.wikipedia.org/wiki/Brunei_Darussalam_Central_Bank
But maybe it doesn't matter that much? Since it's the Sultan, who signed the banknote, according to what I can find on Moneypedie at least.
Sources:
http://www.banknote.ws/COLLECTION/countries/ASI/BRU/BRU.htm
https://en.wikipedia.org/wiki/Brunei_dollar
https://en.wikipedia.org/wiki/Brunei_Darussalam_Central_Bank
