Two parts, viz. vai at the bottom and GD88 at the top.

That there is water down below, the source where the sun fetches it water, was known to the Maya Indians.

Saturn is located there. In the wet darkness.

GD88 could have something to do with the four cardinal points or directions. Or it could show - in analogue with the head sign in the Venus glyph - the extreme points where the planet Saturn could be observed. Also it shows a sign similar to the cross sign of a ruler, the ruler over the four directions.

And there might be an allusion to the four berries in GD21.