Green’s Dictionary of Slang

pongo n.2

[? that adopted by a soldier, i.e. pongo n.1 (2)]

(Aus.) a flowing moustache.

[Aus]Advocate (Burnie, Tas.) 5 June 7/2: Browney’ll be growing a ziff next. What’s it going to be – a tassy or a pongo? [...] ‘tassy,’ toothbrush moustache; ‘pongo,’ flowing moustache.