Grey Global Group set 52-week highs as volume in the normally lightly traded stock tripled Friday. There was no specific news to explain the activity. Grey's price has jumped $100, to more than $550, since the June announcement that Publicis was acquiring Saatchi & Saatchi
. That deal heightened speculation Grey would be an acquisition or merger target. The stocks of True North Communications, Interpublic Group of Cos. and Omnicom Group also rose. In trading Friday, Grey closed at $554.00, up 6.19% for the week.