BlackBerry Ltd.'s Director of Global Public Policy; Mark Cameron is leaving the company to join the PR firm Hill & Knowlton. Cameron will be the new deputy leader of Hill and Knowlton Strategies in January. Cameron is a former aide to Canadian Prime Minister Stephen Harper, joined BlackBerry in 2011. This is the newest departure of an executive from the struggling firm last money Chief Financial Officer Brian Bidulka, Chief Marketing Officer Frank Boulben and Chief Operating Officer Kristian Tear.