Blockdata Command not working with scoreboard (Minecraft 1.10)
Solution 1:
The command works in 1.9.2 and below:
The problem you are having is caused by bug [MC-101457] in 1.9.3 and later. Unfortunately, the solution is to wait for Mojang to get around to fixing it.
In the meantime, scores in /tellraw still work, so as an alternative, you could potentially have right-clicking the sign give the scores in chat.