What's on the sign?
The letters are on the sign.
   src        edge_attr  dst
0    0               on    7
1    1   to the left of    6
2    1   to the left of    7
3    2   to the left of    7
4    5   to the left of    7
5    6  to the right of    1
6    7               on    6
7    7  to the right of    1
8    7  to the right of    5
9    7  to the right of    2