See (ii) below from GM's site...
Trademarks
The marks appearing on this website, including but not limited to: (i) GM and the GM Logo; (ii) Chevrolet, Pontiac, Buick, Cadillac, GMC, Saturn and HUMMER and their respective logos, emblems, slogans and vehicle model names and body designs; and (iii) other marks such as Saab, Holden, Opel, Vauxhall, OnStar, GMAC and ACDELCO are trademarks and/or service marks of General Motors Corporation, its subsidiaries, affiliates or licensors.