1. This is the sign of 'the tired old bird'.
2. The glyph is localized, it seems, at the time of autumn equinox. Perhaps that means it is intended to show that the power of the Sun has gone.
3. If so, then I think we have here a parallel to the meaning of this type of glyph in Sunday. In the daily cycle of the sun 'the tired old bird' presumably represents the time of sunset, in the yearly cycle of the sun 'the tired old bird' presumably represents the time of autumn equinox. Both these times are exactly defined and both implies change from light to dark.
4. So perhaps 'the tired old bird' always should be seen as the declining aspect of the Sun?