The three islets outside Orongo was a characteristic landmark for Easter Island when arriving over the sea, and also a suitable first station for the kuhane flying in from the west:
 
1. Nga Kope Ririva
Ga7-8 (177)

The three ovals in Ga7-8 can make one associate to the three islets:

The vertical straight line in maitaki glyphs is the same element as the 'stem' in poporo:

maitaki poporo

This element (what remains after having taken away the 'seed' at bottom and the 'leafs' at the top end of poporo) probably is what makes poporo a mark of 'birth'.

The maitaki glyph type, therefore, should indicate how the three islets at the beginning of the kuhane journey around the island is the 'birth' place of the new moon, arriving from the horizon in the west.