It depends on where the observer is, if you are following, then you would also be traveling at lightspeed and the turnsignal would appear normally. regardless, if you are able to observe the craft, you will see the turn signal. It would be hard to observe a lightspeed craft at a static point though... I am talking out of my ass right now.
How bout this, if you fell through a shaft that went through the earth, would you just keep flying back and forth as you gained distance from the core?