Ideas:

1. This type of glyph we have seen at the end of the year (winter solstice):

Here it is located as the penulimate glyph in the 6th period after the time of full moon, perhaps indicating the end or death of the moon.

2. But it is part of the penultimate glyph in each period, thereby maybe indicating the end of each such period. I have made a little table over these glyphs.