Ford Motor Co., the second-largest U.S. automaker, said it will protect its script and oval logo from use by supporters of embattled Toronto Mayor Rob Ford.

Rob Ford signed shirts emblazoned with “Ford Nation” incorporating the automaker’s logo at a United Way charity event on Tuesday. The mayor said for the first time today he bought illegal drugs while in office after admitting last week to using crack cocaine and being drunk in public.

“Ford did not grant permission for use of its logo,” Jay Cooney, a company spokesman, said today by telephone. “We view it as an unauthorized use of our trademark and have asked it to be stopped.”

Ford reclaimed control of its logo last year after using it and other assets as collateral to borrow $23.4 billion in 2006 that allowed the company to weather the global financial crisis.

The Dearborn, Michigan-based company regained control after Moody’s Investors Service became the second major ratings company to upgrade the carmaker to investment grade.

Rob Ford’s revelation today that he purchased illegal drugs while in office came amid questioning at a city hall meeting in which a majority of city councilors asked him to take a leave of absence to address his “challenges.”

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