1)Everyone remembers this thing right?
(Well, I'm not yet sure if someone came up with this theory yet but....)
The people that each symbol represents are a part of Bill's master plan (like pawns or maybe his puppets in a sooner time.)
2) Linking to the last part in the first theory (but I'm guessing other people already said this in the internet), Dipper was always been Bill's puppet since Sock Opera
(or maybe Dreamscapers because that episode is Bill's first appearance and Bill confirmed in Sock Opera that he was been keeping an eye on Dipper ever since).
Note: This Journal entry will be updated at a later time if there are other theories in all that.
REMEMBER, REALITY IS AN ILLUSION. THE UNIVERSE IS A HOLOGRAM. BUY GOLD. BYEEE!!!!!!.........