My experience with Signature and Jazz has always been GREAT...
I played a Signature bop set once, and it was fantastic.
It's the same set I'm listening over and over - every year on the Skopje Jazz Festival (a cultural center here owns the set - 18bd, 10tt, 12tt, 14ft, 14x6 snare)
Being mic-d on stage, it's very melodic. Of course, only the best performers use it, so everything sounds great when they play.
But, I must say that with coated Ambassadors top and bottom, it sounds absolutely fantastic.
The only thing that I have as a "bad comment" - they tend to sound thunderous, because of the square depth...
So.... The bottom line - Signatures are great drums. I think that if they weren't square sizes - they'd sound even better...
I think SONOR realized that when they offered Phonics and Sigs side by side. So, as a compromise, they started offering POWER depths.
And with the Designer, they maximized the sound projection and resonance, at the same time minimizing shell/metal contact...
Just my opinion...