Ideas:

Probably this glyph is showing a sign (in the form of a little oval) on top of the apex of the triangle. The sign is not present in the corresponding glyph in Large Santiago. What does this sign mean? Is it the shape of Full Moon? Yes, of course.

But that does not exclude other interpretations. One guess of mine is that it also represents a hole. As seen in Mamari the two staffs of Waxing and Waning Moon perhaps give room for a little hole in the fabric of time/space.

If this is correct, then the logic of signs implies that there ought to be holes wherever we see such small oval shapes among the glyphs, for example as the ears of the person with face front seen in Saturday.