Does anyone know how you can use /setblock to make a sign face what direction you want?
You can do the following command.
For standing signs:
/setblock ~ ~ ~ standing_sign <0-15, each representing a direction.>
For wall signs:
/setblock ~ ~ ~ wall_sign <0-15, each representing a direction.>
0=South, 4=West, 8=North, 12=East
With F3 you can see the rotation on the right side of the debug overlay. Please note that when you put two floating signs together, it will automatically fall off. The reason for this is because when you place the sign on another it automatically updates the first sign causing it to pop off because off no block support then causing the second sign to fall from the first signs update.