impressive, thats some pretty fluid motor control too. Not too jerky or anything.
Im going to venture on the side of pre-recorded movements. The signature signing is just the same thing as a CNC machine except with a pen and a more advance/involved arm controlling it.
As for the violin playing, well that has to be pre-recorded movement. No way did they make a robot that can hear a song being played and pick the next note that would sound good.
Regardless, its still very impressive.