Which states do that?
It's illegal:
http://www.gpo.gov/fdsys/pkg/PLAW-108publ458/pdf/PLAW-108publ458.pdf
SEC. 7214. PROHIBITION OF THE DISPLAY OF SOCIAL SECURITY ACCOUNT NUMBERS ON DRIVER’S LICENSES OR MOTOR VEHICLE REGISTRATIONS.
(a) IN GENERAL.—Section 205(c)(2)(C)(vi) of the Social Security Act (42 U.S.C. 405(c)(2)(C)(vi)) is amended—
(1) by inserting ‘‘(I)’’ after ‘‘(vi)’’; and
(2) by adding at the end the following new subclause: ‘‘(II)
Any State or political subdivision thereof (and any person acting as an agent of such an agency or instrumentality),
in the administration of any driver’s license or motor vehicle registration law within its jurisdiction, may not display a social security account number issued by the Commissioner of Social Security (or any derivative of such number)
on any driver’s license, motor vehicle registration, or personal identification card (as defined in section 7212(a)(2) of the 9/11 Commission Implementation Act of 2004), or include, on any such license, registration, or personal identifica- tion card, a magnetic strip, bar code, or other means of communica-
tion which conveys such number (or derivative thereof).’’.