This type of glyph shows a plant.

In Bishop Jaussen's comments on the readings of Metoro he says that this (poporo) is a plant (called Vergerette by Jaussen) which gave a black pigment used for tattooing. Cfr also the other plant poporo which gave black pigment (Solanum nigrum) for tattooing.

Possibly the double wedge at top is a sign of blackness emerging, an inverted sign for blackness.