Her signature shot is her Serve.
However Vaidisova already did the serve for the Signature Shot series so I guess they couldn't do another serve.
If you look on youtube you will find James Blake signature shot forehand, Vaidisova sig shot serve
Serena's serve is definitely her signature shot. She can flatten it out and place it on a dime. She has very good topspin on her kick serve. The shot is solid and just doesn't break down. The technique is simple and the motion is fluid from the ball toss to her knee bend.
I think her best shot is her serve too but her backhand's nothing to turn your nose up.....although..... why they didn't do "you know who" is beyond me (or maybe they'll use her for the volley, since those are pretty good).
So who's done one:
Career Grand Slam in your 20s? Been there done that. Career golden slam your 30s?