http://www.dmv.ca.gov/pubs/vctop/d12/vc27315_5.htm 27315.5. All law enforcement agencies shall, not later than January 1, 1991, establish a policy and issue an order, in writing, which states whether or not their officers are required to wear seat belts. When a law enforcement agency is developing a safety belt policy, the agency shall consider the officer's safety, comfort, and convenience.
Added Ch. 33, Stats. 1990. Effective March 26, 1990.
And I know they don't have to wear them here!