Publicis CEO Maurice Levy & Omnicom CEO John Wren

Publicis CEO Maurice Levy & Omnicom CEO John Wren

Balint Porneczi/Bloomberg

Publicis Groupe SA Chief Executive Officer Maurice Levy, left, and Omnicom Group Inc. Chief Executive Officer John Wren shake hands after signing the merger during a news conference held on the rooftop of the Publicis headquarters in Paris, on July 28, 2013.