The trouble with interpretating Egyptian symbols is that they're so old the meanings have changed over the centuries and Seshat's "STAR" is a fine example. Seshat was the daughter of Thoth and a goddess of wisdom and scribes. Some of you may be thinking it looks like the underside of a parasol. Sorry.
The egyptians didnt have them so that's not it? Is it a flower ? NO not with seven petals!
My best guess ? While not as astrology obsessed as the ancient Mesopotamians the Egyptians did have stories about the Pleiades. I think its the Seven Stars of the Pleaides linked with the stem linking Seshat to the stars and the shape on the top is the vault of heaven or a horizon line? There are other theories though!
Maybe its a sun or planet or represents the Seven Planets known to the Ancients which were :
The Sun Moon Mercury Mars Jupiter and Saturn.
Maybe there is no ONE TRUE explanation or Meaning?
Think about the differences between Modern Hinduism and the simpler rituals described in Vedic texts.
I suspect if you could interview both one of the priests who "explained" Egyptian religion to Herodotus or Plutarch and then interview a priest from the earliest dynasties they would have VERY different explanations?