Ummmm, manki is mangi. Really. Just a different spelling.
I've been living here for 13 years (as of yesterday, but unfortunately soon to depart) and visiting since '94 and I don't pretend to understand all that is PNG but I can't see that a tok ples reference would mean anything on the side of the aircraft.
Clearly it is a pidgin phrase, my attempt at translating could be wrong.
I just asked the closest PNGean who said it means someone who stayed in the village, a true local.