Well, this is my theory on what it is.
If we think back to Day 6 with Roxas in KHII, Roxas (when he's in the old mansion) draws on a table with a crayon.
Personally, i dont understand why but there are three circles. One of the circles has the Heartless symbol, one of the circles has the Nobodies symbola and the third circle, Roxas draws a sort of crown shape (it has three points) THIS would make sense for it to be the Unbirth symbol. But how Roxas knows this should be unclear.
Heres the Youtube video of Day 6. YouTube - kingdom hearts 2 twilight town day 6 Watch from 7:20 - 7:40. Only for a split second do you see what he draws.
If we think back to Day 6 with Roxas in KHII, Roxas (when he's in the old mansion) draws on a table with a crayon.
Personally, i dont understand why but there are three circles. One of the circles has the Heartless symbol, one of the circles has the Nobodies symbola and the third circle, Roxas draws a sort of crown shape (it has three points) THIS would make sense for it to be the Unbirth symbol. But how Roxas knows this should be unclear.
Heres the Youtube video of Day 6. YouTube - kingdom hearts 2 twilight town day 6 Watch from 7:20 - 7:40. Only for a split second do you see what he draws.