Ideas:

1. I have earlier guessed that this might be a picture of a reinga. My intuition evidently told me that Saturday was the time of death and the association to reinga therefore is reasonable. The Chinese (and Japanese) sign for earth or soil is used when writing Saturday, it is the day of the soil. The sign looks like a cross planted on a grave.

(Source: Kenneth G. Henshall "A Guide to Remembering Japanese Characters".)

2. Possibly this rongorongo glyph is also showing the the soil. In Saturday it is time to return to dust, from whence you came.