Changing the signs blockdata by using Json format doesn't work correctly.
(or did I missed something new with signs ?)

Changing a sign with the command blockdata (in commandblock) with Json format... /blockdata ~ ~1 ~ {Text2:"

"}

Sign reads then

instead of Bye

I think you know how to do it but anyway...
1. Put command block under a sign...
2. type a command to change the sign via Json tag (like blockdata)
3. power commandblock

I hope I didn't miss something out of the latest snapshots and didn't wasted your time now.

I hope you'll see this soon enought, I'm trying to make a map for 1.9