OMC ▼ -3.1% - Omnicom Group Inc. $OMC - Omnicom Advertising Announces Leadership Transition Omnicom Group fell 3.1% today following an announcement of a leadership transition within its advertising division. Leadership changes at major ad firms can prompt investor concern about strategic direction and operational continuity, particularly if they signal broader organizational shifts or uncertainty about management's vision. 09-SEP-2026 10:31 AM ET