Since I'm living in US for (2)years, I still don't remember that each state has own laws. Thank to my friend and colleague Sean I finally understood why Scantegrity cannot be used in California.
These are the two main laws issues :
13204. (a) "All distinguishing marks or erasures are forbidden and
make the ballot void."
14287. "No voter shall place any mark upon a ballot that will make
that ballot identifiable."
Here the official voting codes: Voting Machine dir. (Section 13280-13289), Election Code dir. (13200-13220) and some exceptions (Section 13230-13233).
For people that don't know how scantegrity works here a nice graphical summary.
As you see in the figure above, people have to mark the ballot ("Waht Voter Leaves in the Ballot Box") and people could keep a voting proof (A: "What Voter Takes Home").