New York-based Omnicom said vice chairman Tom Watson is retiring from the company, effective Jan. 1. Watson, 70, joined BBDO in 1966, 20 years before Omnicom was formed. In 1986, the agency joined with DDB Needham and Chiat/Day to form the holding company. That same year, Watson moved into Omnicom as president and COO of the Diversified Agency Services group. An Omnicom rep said he would not be replaced.